Merge branch 'update/rouge-2.0.6' into 'master'

update rouge to 2.0.6

## What does this MR do?

Bumps rouge to 2.0.6

## Are there points in the code the reviewer needs to double check?

Changelog here: https://github.com/jneen/rouge/blob/master/CHANGELOG.md#version-206-2016-09-07


## Why was this MR needed?

## Screenshots (if relevant)

## Does this MR meet the acceptance criteria?

- [ ] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [ ] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [ ] API support added
- Tests
  - [ ] Added for this feature/bug
  - [ ] All builds are passing
- [ ] Conform by the [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [ ] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [ ] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [ ] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

## What are the relevant issue numbers?

See merge request !6251

CHANGELOG

 Please view this file on the master branch, on stable branches it's out of date.
 
 v 8.12.0 (unreleased)
+  - Update the rouge gem to 2.0.6, which adds highlighting support for JSX, Prometheus, and others. !6251
   - Add ability to fork to a specific namespace using API. (ritave)
   - Cleanup misalignments in Issue list view !6206
   - Prepend blank line to `Closes` message on merge request linked to issue (lukehowell)

Gemfile.lock

@@ -584,7 +584,7 @@ GEM
       railties (>= 4.2.0, < 5.1)
     rinku (2.0.0)
     rotp (2.1.2)
-    rouge (2.0.5)
+    rouge (2.0.6)
     rqrcode (0.7.0)
       chunky_png
     rqrcode-rails3 (0.1.7)