This allows us to drop our disable email config override

See:

https://github.com/mperham/sidekiq/blob/master/Changes.md#413
https://gitlab.com/gitlab-org/gitlab-ce/issues/19441

Includes Rails 5 support and various bug fixes.

Changelog: https://github.com/doorkeeper-gem/doorkeeper/blob/master/NEWS.md#400

Also upgrade its dependencies. Includes Rails 5 support.

Changelogs:
rspec-rails: https://github.com/rspec/rspec-rails/compare/v3.4.2...v3.5.0
rspec-core: https://github.com/rspec/rspec-core/compare/v3.4.0...v3.5.0
rspec-support: https://github.com/rspec/rspec-support/compare/v3.4.0...v3.5.0
rspec-expectations: https://github.com/rspec/rspec-expectations/compare/v3.4.0...v3.5.0
rspec-mocks: https://github.com/rspec/rspec-mocks/compare/v3.4.0...v3.5.0
rspec: https://github.com/rspec/rspec/compare/v3.4.0...v3.5.0

Includes support for Rack 2.

Changelog: https://github.com/macournoyer/thin/blob/master/CHANGELOG

Adds a dependency on Sinatra and allows Sinatra 2 for eventual support of Rack 2.

Changelog: https://github.com/mperham/sidekiq/blob/master/Changes.md#414

Adds Rails 5 support.

Changelog: https://github.com/mbleigh/seed-fu/blob/master/CHANGELOG.md#version-236

Changelog: https://github.com/intridea/oauth2/compare/v1.0.0...v1.2.0

Follow-up on !3434 since 1.2.0 doesn't limit the JWT version we can use.

Upgrade sass-rails from 5.0.4 to 5.0.5. Includes support for Rails 5.

Changelog: https://github.com/rails/sass-rails/releases

quiet_assets has been seemingly abandoned, and now sprockets-rails has the feature built-in!

From this PR: https://github.com/rails/sprockets-rails/pull/355

Upgrade Sprockets from 3.6.0 to 3.6.2.

Changelog: https://github.com/rails/sprockets/blob/3.x/CHANGELOG.md

Upgrade Sprockets Rails from 3.0.4 to 3.1.1.

Changelog: https://github.com/rails/sprockets-rails/compare/v3.0.4...v3.1.1

No reason to split it into a separate gem when the gem barely did anything. We can use gemojione directly, making updating gemojione that much easier.

Also fix the Rake task and update gemojione to 2.6.1. This adds the EmojiOne Spring update.

Changelog: https://github.com/jonathanwiesel/gemojione/blob/master/CHANGELOG.md

Changelog: https://github.com/getsentry/raven-ruby/releases