Decoding error on license file on macOS

Same issue as #35 and #37 but on macOS with a standard Python 3 install, not in a docker container.

Tested on 1.16.1.

$ pip-licenses --from=mixed --with-system --format=rst --with-license-file
Traceback (most recent call last):
  File "/Users/user/proj/.tox/licenses/bin/pip-licenses", line 8, in <module>
    sys.exit(main())
  File "/Users/user/proj/.tox/licenses/site-packages/piplicenses.py", line 638, in main
    print(output_string)
  File "/Users/user/proj/.tox/licenses/lib-python/3/encodings/ascii.py", line 22, in encode
    return codecs.ascii_encode(input, self.errors)[0]
UnicodeEncodeError: 'ascii' codec can't encode character '\xa9' in position 167881: ordinal not in range(128)

Python prompt for reference:

$ python
Python 3.6.9 (5da45ced70e5, Oct 09 2019, 19:13:07)
[PyPy 7.2.0 with GCC 4.2.1 Compatible Apple LLVM 10.0.0 (clang-1000.11.45.5)] on darwin
Type "help", "copyright", "credits" or "license" for more information.

[raimon49]

I add to the documentation as a frequently asked question about UnicodeEncodeError.

Your report was very helpful. Thanks a lot!

[johnthagen]

[testenv]
passenv= LC_CTYPE

fixed it, thanks!

Still strange though. I suppose that it’s because tox doesn’t bring in any ENV variables by default. But, then again lots of Python programs can read Unicode files from within tox, so I wonder if there is a way to make pip-licenses work out of the box? It seems like if it’s reading arbitrary license files from PyPI it shouldn’t really need to assume the user has a certain locale?

Hmm, not sure, but really appreciate the fix!