Fix lint errors

src/drf_yasg/openapi.py

@@ -167,7 +167,7 @@ class SwaggerDict(OrderedDict):
     def __reduce__(self):
         # for pickle supprt; this skips calls to all SwaggerDict __init__ methods and relies
         # on the already set attributes instead
-        attrs = {k: v for k ,v in vars(self).items() if not k.startswith('_NP_')}
+        attrs = {k: v for k, v in vars(self).items() if not k.startswith('_NP_')}
         return _bare_SwaggerDict, (type(self),), attrs, None, iter(self.items())