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/persisters/filesystem.py

@@ -5,14 +5,13 @@ from ..serialize import serialize, deserialize
 
 
 class FilesystemPersister(object):
-
     @classmethod
     def load_cassette(cls, cassette_path, serializer):
         try:
             with open(cassette_path) as f:
                 cassette_content = f.read()
         except IOError:
-            raise ValueError('Cassette not found.')
+            raise ValueError("Cassette not found.")
         cassette = deserialize(cassette_content, serializer)
         return cassette
 
@@ -22,5 +21,5 @@ class FilesystemPersister(object):
         dirname, filename = os.path.split(cassette_path)
         if dirname and not os.path.exists(dirname):
             os.makedirs(dirname)
-        with open(cassette_path, 'w') as f:
+        with open(cassette_path, "w") as f:
             f.write(data)