update sprockets version

Upgrade unicorn from 4.9.0 to 5.1.0 and unicorn-worker-killer from 0.4.2 to 0.4.4.

Changelog for unicorn: http://unicorn.bogomips.org/NEWS.html

Changelog for unicorn-worker-killer: https://github.com/kzk/unicorn-worker-killer/blob/bdec225f028d1bda01b5888578c479b0c705f1a8/ChangeLog

This reverts commit 70faf5fd, reversing
changes made to 2307eb84.

It's mainly intended to improve Elasticsearch indexing performance
(through multi_json gem), but other gems could benefit from it too, like
grape.

Changelog:
https://github.com/mperham/sidekiq/blob/921e939f995fbb5238975d4121d728b95be99ab5/Changes.md#421

Sinatra is no longer required and sidekiq uses a vanilla Rack app for
its Web UI now.

Signed-off-by: NRémy Coutable <remy@rymai.me>

This allows us to take advantage of
https://gitlab.com/gitlab-org/gitlab_git/merge_requests/121.

If `git gc` runs and `Repository` has an instance to `Rugged::Repository`, a
bug in libgit2 may cause the instance to return a stale value or a missing
branch. This change not only optimizes the branch lookup so we don't have
to iterate through every branch, but it also works around the `git gc`
issue by forcing a repository reload every time `Repository#find_branch`
is called.

See: https://github.com/libgit2/libgit2/issues/1534

Closes #15392, #21470

Changelog: https://git.io/v6PnV

Fixes gitlab-org/gitlab-ce#21025 and gitlab-org/gitlab-ce#21017

- Return only slash commands that make sense for the current noteable
- Allow slash commands decription to be dynamic

Other improvements:

- Add permission checks in slash commands definition
- Use IssuesFinder and MergeRequestsFinder
- Use next if instead of a unless block, and use splat operator instead of flatten
Signed-off-by: NRémy Coutable <remy@rymai.me>

More information available at: http://weblog.rubyonrails.org/2016/8/11/Rails-5-0-0-1-4-2-7-2-and-3-2-22-3-have-been-released/

Changelog: https://github.com/ruby-grape/grape/blob/v0.15.0/CHANGELOG.md

Works toward #18226.

Bug fixes and compatibility with Rails 5.

Changelog: https://github.com/newrelic/rpm/blob/master/CHANGELOG

This includes support for Rails 5 without deprecations warnings.

Changelog: https://github.com/DatabaseCleaner/database_cleaner/blob/master/History.rdoc#153-2016-04-22

Removes methods that were deprecated in Rails 5.

Changelog: https://github.com/flyerhzm/bullet/blob/master/CHANGELOG.md#520

Fixed issue with resolve buttons always being visible - even when not logged in