Merge branch '18593-update-rinku' into 'master'

Bump Rinku to 2.0.0

## What does this MR do?

Update Rinku gem to last stable version.

## What are the relevant issue numbers?

#18593 

## Does this MR meet the acceptance criteria?

- [x] [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~~
  - [x] All builds are passing
- [x] Conform by the [style guides](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CONTRIBUTING.md#style-guides)
- [x] Branch has no merge conflicts with `master` (if you do - rebase it please)
- [x] [Squashed related commits together](https://git-scm.com/book/en/Git-Tools-Rewriting-History#Squashing-Commits)

See merge request !5064

CHANGELOG

@@ -27,6 +27,7 @@ v 8.10.0 (unreleased)
   - PipelinesFinder uses git cache data
   - Check for conflicts with existing Project's wiki path when creating a new project.
   - Don't instantiate a git tree on Projects show default view
+  - Bump Rinku to 2.0.0
   - Remove unused front-end variable -> default_issues_tracker
   - Better caching of git calls on ProjectsController#show.
   - Add API endpoint for a group issues !4520 (mahcsig)

Gemfile.lock

@@ -576,7 +576,7 @@ GEM
       listen (~> 3.0)
     responders (2.1.1)
       railties (>= 4.2.0, < 5.1)
-    rinku (1.7.3)
+    rinku (2.0.0)
     rotp (2.1.2)
     rouge (1.11.0)
     rqrcode (0.7.0)