Merge pull request #538 from tymofij/require-modern-oauthlib

add minimal oauthlib requirement

requirements.txt

@@ -5,3 +5,4 @@ lxml>=3.1.0
 Pillow
 python-dateutil
 python-social-auth>=0.1.17,<0.1.24
+oauthlib>=0.6.3