Fixing a failing test (failure caused by a change made in google-auth v1.1.1 that went out today) (#75)

Author: hiranya911

tests/test_credentials.py

@@ -29,7 +29,7 @@
 
 
 def check_scopes(g_credential):
-    assert isinstance(g_credential, google.auth.credentials.Scoped)
+    assert isinstance(g_credential, google.auth.credentials.ReadOnlyScoped)
     assert sorted(credentials._scopes) == sorted(g_credential.scopes)