Monkeypatch deprecated omniauth-github behaviour

[DazWorrall]

Fixes #1011

The issue is in omniauth-github but it is currently unmaintained, so this patches in the fix which is unlikely to be merged any time soon.

This patch has been installed successfully on other apps at Shopify.

[casperisfine]

Quick update:

• The unmaintained notice seem outdated: Update README.md omniauth/omniauth-github#85, so there's hope it will be fixed upstream some time soon.
• In the meantime Shipit users can put gem 'omniauth-github', github: 'DazWorrall/omniauth-github', branch: 'query-auth-deprecated' in their Gemfile.
• If the PR isn't merged in a few days / weeks, then we can consider other options.

[casperisfine]

We managed to get the fix upstream and released.

Closing this

Ref: #1011