Can't lock package with `git` and `extras`

Issue description

A package spec with git and extras fails to lock. This happens regardless of the editable flag.

Expected result

The package should be installed with all extras.

Actual result

[I] ~/test $ pipenv --version
pipenv, version 2018.7.1
[I] ~/test $ ll
total 8
-rw-r--r--  1 jacobhayes    96B Jul  3 13:12 Pipfile
[I] ~/test $ cat Pipfile
[packages]
requests = {git = "https://github.com/requests/requests.git", extras = ["security"]}
[I] ~/test $ pipenv --rm ; pipenv install --verbose
Removing virtualenv (/Users/jacobhayes/.local/share/virtualenvs/test-qFl43Lkt)...
Creating a virtualenv for this project...
Pipfile: /Users/jacobhayes/test/Pipfile
Using /usr/local/opt/python/bin/python3.6 (3.6.5) to create virtualenv...
⠋Already using interpreter /usr/local/opt/python/bin/python3.6
Using base prefix '/usr/local/Cellar/python/3.6.5/Frameworks/Python.framework/Versions/3.6'
New python executable in /Users/jacobhayes/.local/share/virtualenvs/test-qFl43Lkt/bin/python3.6
Also creating executable in /Users/jacobhayes/.local/share/virtualenvs/test-qFl43Lkt/bin/python
Installing setuptools, pip, wheel...done.
Setting project for test-qFl43Lkt to /Users/jacobhayes/test

Virtualenv location: /Users/jacobhayes/.local/share/virtualenvs/test-qFl43Lkt
Pipfile.lock not found, creating...
Locking [dev-packages] dependencies...
Locking [packages] dependencies...
Traceback (most recent call last):
  File "/usr/local/bin/pipenv", line 11, in <module>
    sys.exit(cli())
  File "/usr/local/lib/python3.6/site-packages/pipenv/vendor/click/core.py", line 722, in __call__
    return self.main(*args, **kwargs)
  File "/usr/local/lib/python3.6/site-packages/pipenv/vendor/click/core.py", line 697, in main
    rv = self.invoke(ctx)
  File "/usr/local/lib/python3.6/site-packages/pipenv/vendor/click/core.py", line 1066, in invoke
    return _process_result(sub_ctx.command.invoke(sub_ctx))
  File "/usr/local/lib/python3.6/site-packages/pipenv/vendor/click/core.py", line 895, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/usr/local/lib/python3.6/site-packages/pipenv/vendor/click/core.py", line 535, in invoke
    return callback(*args, **kwargs)
  File "/usr/local/lib/python3.6/site-packages/pipenv/cli.py", line 435, in install
    selective_upgrade=selective_upgrade,
  File "/usr/local/lib/python3.6/site-packages/pipenv/core.py", line 1943, in do_install
    pypi_mirror=pypi_mirror,
  File "/usr/local/lib/python3.6/site-packages/pipenv/core.py", line 1312, in do_init
    pypi_mirror=pypi_mirror,
  File "/usr/local/lib/python3.6/site-packages/pipenv/core.py", line 1140, in do_lock
    project.write_lockfile(lockfile)
  File "/usr/local/lib/python3.6/site-packages/pipenv/project.py", line 648, in write_lockfile
    content, indent=4, separators=(u',', u': '), sort_keys=True,
  File "/usr/local/Cellar/python/3.6.5/Frameworks/Python.framework/Versions/3.6/lib/python3.6/json/__init__.py", line 238, in dumps
    **kw).encode(obj)
  File "/usr/local/Cellar/python/3.6.5/Frameworks/Python.framework/Versions/3.6/lib/python3.6/json/encoder.py", line 201, in encode
    chunks = list(chunks)
  File "/usr/local/Cellar/python/3.6.5/Frameworks/Python.framework/Versions/3.6/lib/python3.6/json/encoder.py", line 430, in _iterencode
    yield from _iterencode_dict(o, _current_indent_level)
  File "/usr/local/Cellar/python/3.6.5/Frameworks/Python.framework/Versions/3.6/lib/python3.6/json/encoder.py", line 404, in _iterencode_dict
    yield from chunks
  File "/usr/local/Cellar/python/3.6.5/Frameworks/Python.framework/Versions/3.6/lib/python3.6/json/encoder.py", line 404, in _iterencode_dict
    yield from chunks
  File "/usr/local/Cellar/python/3.6.5/Frameworks/Python.framework/Versions/3.6/lib/python3.6/json/encoder.py", line 404, in _iterencode_dict
    yield from chunks
  File "/usr/local/Cellar/python/3.6.5/Frameworks/Python.framework/Versions/3.6/lib/python3.6/json/encoder.py", line 437, in _iterencode
    o = _default(o)
  File "/usr/local/Cellar/python/3.6.5/Frameworks/Python.framework/Versions/3.6/lib/python3.6/json/encoder.py", line 180, in default
    o.__class__.__name__)
TypeError: Object of type 'ArrayElement' is not JSON serializable

Steps to replicate

[packages]
requests = {git = "https://github.com/requests/requests.git", extras = ["security"]}

pipenv install

---

$ pipenv --support

Pipenv version: '2018.7.1'

Pipenv location: '/usr/local/lib/python3.6/site-packages/pipenv'

Python location: '/usr/local/opt/python/bin/python3.6'

Other Python installations in PATH:

• 2.7: /usr/local/bin/python2.7

• 2.7: /usr/local/bin/python2.7

• 2.7: /usr/bin/python2.7

• 3.6: /usr/local/bin/python3.6m

• 3.6: /usr/local/bin/python3.6

• 2.7.15: /usr/local/bin/python

• 2.7.10: /usr/bin/python

• 2.7.15: /usr/local/bin/python2

• 3.6.5: /usr/local/bin/python3

PEP 508 Information:

{'implementation_name': 'cpython',
 'implementation_version': '3.6.5',
 'os_name': 'posix',
 'platform_machine': 'x86_64',
 'platform_python_implementation': 'CPython',
 'platform_release': '17.6.0',
 'platform_system': 'Darwin',
 'platform_version': 'Darwin Kernel Version 17.6.0: Tue May  8 15:22:16 PDT '
                     '2018; root:xnu-4570.61.1~1/RELEASE_X86_64',
 'python_full_version': '3.6.5',
 'python_version': '3.6',
 'sys_platform': 'darwin'}

System environment variables:

• Apple_PubSub_Socket_Render
• COLORFGBG
• COLORTERM
• COPYFILE_DISABLE
• EDITOR
• GOPATH
• HOME
• ITERM_PROFILE
• ITERM_SESSION_ID
• LANG
• LOGNAME
• PAGER
• PATH
• PWD
• SECURITYSESSIONID
• SHELL
• SHLVL
• SSH_AUTH_SOCK
• TERM
• TERM_PROGRAM
• TERM_PROGRAM_VERSION
• TERM_SESSION_ID
• TMPDIR
• TMUX
• TMUX_PANE
• TMUX_PLUGIN_MANAGER_PATH
• USER
• XPC_FLAGS
• XPC_SERVICE_NAME
• __CF_USER_TEXT_ENCODING
• PYTHONDONTWRITEBYTECODE
• PIP_PYTHON_PATH

Pipenv–specific environment variables:

Debug–specific environment variables:

• PATH: /Users/jacobhayes/bin:/Users/jacobhayes/bin:/usr/local/Caskroom/google-cloud-sdk/latest/google-cloud-sdk/bin:/Users/jacobhayes/bin:/usr/local/bin:/usr/bin:/bin:/usr/sbin:/sbin
• SHELL: /usr/local/bin/fish
• EDITOR: vim
• LANG: en_US.UTF-8
• PWD: /Users/jacobhayes/test

---

Contents of Pipfile (‘/Users/jacobhayes/test/Pipfile’):

[packages]
requests = {git = "https://github.com/requests/requests.git", extras = ["security"]}

[theunraveler]

This bug is a 3.7+ bug and should only be happening since the combination of 3.7 + 2018.7.1.

This is definitely happening on 3.6.* for me.

[bryanforbes]

@JacobHayes you’re more than welcome to do the PR. I’m swamped this week.