Apply fix from 3b10868 to users tests too

Repeat after me "I'll run a full test suite before pushing changes"

pinry/users/tests.py

@@ -10,7 +10,7 @@ from .models import User
 
 
 def mock_requests_get(url):
-    response = mock.Mock(content=open('logo.png').read())
+    response = mock.Mock(content=open('logo.png', 'rb').read())
     return response