DOC: remove references to oauth2client (#61)

Closes #59.

Author: tswast

docs/source/install.rst

@@ -39,4 +39,6 @@ This module requires following additional dependencies:
 
 - `httplib2 <https://github.com/httplib2/httplib2>`__: HTTP client
 - `google-api-python-client <http://github.com/google/google-api-python-client>`__: Google's API client
-- `oauth2client <https://github.com/google/oauth2client>`__: authentication and authorization for Google's API
+- `google-auth <https://github.com/GoogleCloudPlatform/google-auth-library-python>`__: authentication and authorization for Google's API
+- `google-auth-oauthlib <https://github.com/GoogleCloudPlatform/google-auth-library-python-oauthlib>`__: integration with `oauthlib <https://github.com/idan/oauthlib>`__ for end-user authentication
+- `google-auth-httplib2 <https://github.com/GoogleCloudPlatform/google-auth-library-python-httplib2>`__: adapter to use ``httplib2`` HTTP client with ``google-auth``