ruby 2.0.x required for gitlab 7.0+

Update omniauth-google-oauth2 gem

#### What does this MR do?

This PR updates google omniauth gem.

#### Why was this MR needed?

This is needed, because google deprecates some API on Sept, 1st.

All tests pass, but I still have to ~~test and update documentation in https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/integration/google.md~~

**Contacts API" and "Google+ API need to be enabled**

This need to be stated in the update guide (7.1 to 7.2), as well as (6.0 to 7.2)

This fixes #512

See merge request !171

API: Labels validation in issues API

Skipping rc3 because somebody (me) created a tag but did not bump the
version to rc3.

Fix project description on explore page, fixes #7458

use default white-space for sidebar buttons, fixes #7549

Fix color toggle for labels in edit view

Fix label migration

Failure to create any labels at all caused this DB migration to run for over 40
minutes during a gitlab.com deploy this morning. This change specifies a color f
or each new label and strips invalid characters from the label name.

See merge request !1024

Add oauth doc to 6.0 to 7.2 upgrader

Udate doc

Add dealing with newlines for editor to 5.1-to-6.0

Fix env variable style for documentation

Add missing elements to webhook doc

Fix minor spelling error in repo settings page

API: Fix labels return code

Update gems with errors, to prevent 500 errors

Consistency: Capitalize hex values of sugested colors

Fix Md style for API.

Fix Md style for projects API doc.

Fix grammar and spelling

Consistency, spelling and grammar