Format project with black (#467)

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

vcr/stubs/compat.py

@@ -1,6 +1,7 @@
 import six
 from six import BytesIO
 from six.moves.http_client import HTTPMessage
+
 try:
     import http.client
 except ImportError: