fix syntax error on 2.1 and rubocop on 2.2

Background:

Hashes `{:'key': 'value'}` are not valid in 2.1 but are recommended by Rubocop on 2.2. We only use those when we have a key such as `weird-key`, `weird.key`, etc... 

We could disable Rubocop but it wouldn't warn us about the recommended syntax since `Ruby 1.9`: `{key: 'value'}`, which is valid for `Ruby 1.9+`.

Workaround 1 could be disabling `Style/HashSyntax:` in `rubocop.yml`. 

Workaround 2 (tried in this MR) is to trick Rubocop using `.to_sym` which is effectively the same as adding the `:`. This would allow to keep the warning in place.

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/12801

See merge request !2637

Correctly determine MR diff base when MR has merge conflicts

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/12779

See merge request !2632

Fix highlighting in blame view.

See merge request !2630

Backport LDAP user assignment changes from EE

See https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/146

See merge request !2641

Update sentry-raven gem.

Should resolve `fatal: Not a git repository (or any of the parent directories): .git` warnings.

Fixes #12657

See merge request !2636

See https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/146

Show list of forks for a given Project

Closes #2406

See merge request !2376

Save list sort in a cookie

Closes #5546 

See merge request !2537

Fix preventing migration from crashing in very specific cases

Closes #12606. Closes #12501.

/cc @yorickpeterse @dbalexandre 

See merge request !2600

Improve consistency and duplication for Merge Request API

* Follow REST for merge request API route
* Remove repeating comments API for MR
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Fixes #4759 and #11810 

See merge request !2639

Removed sorted text from dropdowns

![Screen_Shot_2016-01-28_at_09.04.36](/uploads/9e0e1fdb45ad12d122f860a2164d9396/Screen_Shot_2016-01-28_at_09.04.36.png)

Closes #12796 

cc @creamzy @jschatz1 

See merge request !2635

* Follow REST for merge request API route
* Remove repeating comments API for MR
Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Makes ol margin big enough for 3 digits.

Fixes #7960 

![Screen_Shot_2016-01-25_at_11.20.03_PM](/uploads/73c4b9e939fe108fb3b8221e16e686bd/Screen_Shot_2016-01-25_at_11.20.03_PM.png)


See merge request !2608

Adds feature: Ajax Close/Open updates discussion automatically

Triggers jQuery event <br/>
Fixes #5544

See merge request !2610

This ensures that rake tasks that don't need a DB connection can be run
without one.

Return a fake application settings OpenStruct when this is not the case.
Also, use ActiveRecord::Base.connection_pool.active_connection? instead
of ActiveRecord::Base.connection.active? to avoid driver exception.

Closes #12796

[ci skip]

[ci skip]

Update Ruby version to 2.2.4 (latest previous stable) and update docs

Tests and issues added to https://github.com/gitlabhq/gitlabhq/issues/8696 were all fine after the upgrade. 

Main issue: https://gitlab.com/gitlab-org/gitlab-ce/issues/3340

See merge request !2534

Improve performance of retrieving last update times for events

See 75195eefcca4cb3961986c90c8e837da02f30134 and
https://gitlab.com/gitlab-org/gitlab-ce/issues/12415#note_3387317
for the juicy details.

Related issue: https://gitlab.com/gitlab-org/gitlab-ce/issues/12415

See merge request !2613

Skip the 2FA requirement during logout

See merge request !2581

[ci skip]

Increase contrast between highlighted code comments and inline diff marker.

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/12737.

It was especially bad in Monokai, better now.

See merge request !2629

Fix CI runner version not being properly updated when asked for a build

Due to broken implementation of attribute_for_keys the runner information was not updated correctly.

This MR adds test to check that such scenario will never happen again.

See merge request !2618

Return a 404 instead of a 500 when accessing a non-existent group

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/3352

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/5600

See merge request !2614

Limit jquery-ui requires to what we actually use



See merge request !2274

Update wording for 2FA requirement notice



See merge request !2582

Remove link from system hook

Closes #12672

See merge request !2588