DER and pytest fail to run on Windows

[aarondandy]

When trying to work with DER certificates or run the pytests on windows, the script will fail.

tests\test_x509_parser.py:10: in <module>
    object_pairs_hook=OrderedDict)
C:\Program Files\WindowsApps\PythonSoftwareFoundation.Python.3.7_3.7.752.0_x64__qbz5n2kfra8p0\lib\json\__init__.py:293: in load
    return loads(fp.read(),
C:\Program Files\WindowsApps\PythonSoftwareFoundation.Python.3.7_3.7.752.0_x64__qbz5n2kfra8p0\lib\encodings\cp1252.py:23: in decode
    return codecs.charmap_decode(input,self.errors,decoding_table)[0]
E   UnicodeDecodeError: 'charmap' codec can't decode byte 0x81 in position 2948: character maps to <undefined>

as discovered in #8

[jcrowgey]

Whoa, deja vu: insanum/gcalcli#387