Format with line length 110 to match flake8
make black part of linting check
Update travis spec for updated black requirements
Add diff output for black on failure
update changelog
When no cassette exists, it's expected that the response returned, should be
the original, unchanged response. The response recorded in the cassette should be
that which is returned by the before_record_response callback.
But on subsequent requests/responses (when a cassette exists), the responses
returned should be exactly what is in the cassette.
resolves#355
