Fix test fixture encoding

[OttoWinter]

Description:

For the past week, I've constantly been getting errors when running the py.test tests from within PyCharm and ignored them since they had nothing to do with my code. Example:

tests/components/weather/test_darksky.py:29 (TestDarkSky.test_setup)
self = <tests.components.weather.test_darksky.TestDarkSky testMethod=test_setup>
mock_req = <requests_mock.mocker.Mocker object at 0x1032a5dd8>
mock_get_forecast = <MagicMock name='get_forecast' id='4348075424'>

    @requests_mock.Mocker()
    @patch('forecastio.api.get_forecast', wraps=forecastio.api.get_forecast)
    def test_setup(self, mock_req, mock_get_forecast):
        """Test for successfully setting up the forecast.io platform."""
        uri = (r'https://api.(darksky.net|forecast.io)\/forecast\/(\w+)\/'
               r'(-?\d+\.?\d*),(-?\d+\.?\d*)')
        mock_req.get(re.compile(uri),
>                    text=load_fixture('darksky.json'))

test_darksky.py:37: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
../../common.py:250: in load_fixture
    return fptr.read()
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

self = <encodings.ascii.IncrementalDecoder object at 0x1032a3828>
input = b'{\n    "alerts": [\n        {\n            "description": "...BEACH HAZARDS STATEMENT REMAINS IN EFFECT UNTIL 9 PM P...day",\n        "summary": "Clear for the hour."\n    },\n    "offset": -7,\n    "timezone": "America/Los_Angeles"\n}\n'
final = True

    def decode(self, input, final=False):
>       return codecs.ascii_decode(input, self.errors)[0]
E       UnicodeDecodeError: 'ascii' codec can't decode byte 0xc2 in position 10233: ordinal not in range(128)

[...]/lib/python3.6/encodings/ascii.py:26: UnicodeDecodeError

Now I finally took some time to dig into this and manually setting the encoding in load_fixture seems to fix the problem. This shouldn't cause any issues on other systems since all fixtures are encoded with utf-8 anyway.

Side note: Is there any reason we're not using pathlib? I've used it in my own scripts for months now and it's so much easier to use (and probably safer) than doing os.path.join.

Checklist:

• The code change is tested and works locally.
• Local tests with tox run successfully. Your PR cannot be merged unless tests pass

[balloob]

pathlib is just a different way of doing the same thing. People have their preference. And no, there is no reason to migrate all our usages to pathlib 😉