feat: add client_options support for api endpoint override (#829)

* feat: add client_options support for api endpoint override
* chore: replace all `assertEquals` with `assertEqual`
diff --git a/setup.py b/setup.py
index 617515b..82447e8 100644
--- a/setup.py
+++ b/setup.py
@@ -36,6 +36,7 @@
     "httplib2>=0.17.0,<1dev",
     "google-auth>=1.4.1",
     "google-auth-httplib2>=0.0.3",
+    "google-api-core>=1.13.0,<2dev",
     "six>=1.6.1,<2dev",
     "uritemplate>=3.0.0,<4dev",
 ]