Python 3: do not hardcode class name in test_request_stubs_internals().
Python 3: do not hardcode class name in test_request_stubs_internals().

StringIO might be either 'StringIO.StringIO' or 'io.BytesIO' depending on the
version of Python used. Do not hardcode the type in the test.

pxg/HTTPretty,xgess/HTTPretty,BenjamenMeyer/HTTPretty,paylogic/HTTPretty,andresriancho/HTTPretty,gabrielfalcao/HTTPretty,xgess/HTTPretty,BenjamenMeyer/HTTPretty,paylogic/HTTPretty,andresriancho/HTTPretty,xgess/HTTPretty,demianbrecht/HTTPretty,letolab/HTTPretty,Multiposting/HTTPretty,andresriancho/HTTPretty,Multiposting/HTTPretty,demianbrecht/HTTPretty,paylogic/HTTPretty,BenjamenMeyer/HTTPretty,pxg/HTTPretty,letolab/HTTPretty,pxg/HTTPretty,demianbrecht/HTTPretty,Multiposting/HTTPretty,codepython/HTTPretty,codepython/HTTPretty,gabrielfalcao/HTTPretty,codepython/HTTPretty,andresriancho/HTTPretty,letolab/HTTPretty