Update python-social-auth packages

Moves to new Google auth API from deprecated Google+ API

requirements.txt

@@ -48,8 +48,8 @@ requests==2.21.0
 requests-oauthlib==1.0.0
 six==1.11.0
 snowballstemmer==1.2.1
-social-auth-app-django==3.0.0
-social-auth-core==2.0.0
+social-auth-app-django==3.1.0
+social-auth-core==3.1.0
 Sphinx==1.7.6
 sphinx-rtd-theme==0.4.2
 sphinxcontrib-apidoc==0.3.0