Travis build fails for Conda package

See: https://travis-ci.org/pydata/pandas-gbq/jobs/392794382

Per https://github.com/conda-forge/staged-recipes/wiki/Namespace-packages, I think we’ll probably need to create some empty google-namespace and google-cloud-namespace Conda packages.

Applying my previous fix of locking the miniconda version didn’t work this time. (https://github.com/pydata/pandas-gbq/pull/187)

[tswast]

Fixed by https://github.com/pydata/pandas-gbq/pull/234

[tswast]

With CircleCI and the miniconda3 container, the packages are installing okay (that was the problem on Travis). Strangely, the pandas DataFrame is getting Nones instead of float.nans for NULL floating point values.

_____ TestReadGBQIntegration.test_should_properly_handle_null_floats[env] ______

self = <tests.system.test_gbq.TestReadGBQIntegration object at 0x7f9779df0ba8>
project_id = 'pandas-gbq-tests'

    def test_should_properly_handle_null_floats(self, project_id):
        query = "SELECT FLOAT(NULL) AS null_float"
        df = gbq.read_gbq(
            query,
            project_id=project_id,
            credentials=self.credentials,
            dialect="legacy",
        )
>       tm.assert_frame_equal(df, DataFrame({"null_float": [np.nan]}))
...
/opt/conda/envs/test-environment/lib/python3.6/site-packages/pandas/util/testing.py:1010: in assert_attr_equal
    left_attr, right_attr)
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

obj = 'Attributes', message = 'Attribute "dtype" are different'
left = dtype('O'), right = dtype('float64'), diff = None

    def raise_assert_detail(obj, message, left, right, diff=None):
        if isinstance(left, np.ndarray):
            left = pprint_thing(left)
        if isinstance(right, np.ndarray):
            right = pprint_thing(right)
    
        msg = """{0} are different
    
    {1}
    [left]:  {2}
    [right]: {3}""".format(obj, message, left, right)
    
        if diff is not None:
            msg = msg + "\n[diff]: {diff}".format(diff=diff)
    
>       raise AssertionError(msg)
E       AssertionError: Attributes are different
E       
E       Attribute "dtype" are different
E       [left]:  object
E       [right]: float64

/opt/conda/envs/test-environment/lib/python3.6/site-packages/pandas/util/testing.py:1092: AssertionError

See: https://circleci.com/gh/tswast/pandas-gbq/11

I wonder if that is an issue for pandas 0.23.4 in general? It would be a surprising change of behavior if so.