Always ask for email with github omniauth

Fixes: #2061

Fix was proposed on twitter by: neic0, in the following tweet:
https://twitter.com/neic0/status/423138339806392320

config/gitlab.yml.example

@@ -154,7 +154,8 @@ production: &base
       # - { name: 'twitter', app_id: 'YOUR APP ID',
       #     app_secret: 'YOUR APP SECRET'}
       # - { name: 'github', app_id: 'YOUR APP ID',
-      #     app_secret: 'YOUR APP SECRET' }
+      #     app_secret: 'YOUR APP SECRET',
+      #     args: { scope: 'user:email' } }