Merge branch 'modal-mergerequest-shorten-clipboard' into 'master'

edited stylesheet with mr modal fixes and added to changelog

## What does this MR do?
It shortens the modal command merge info elements.

## Are there points in the code the reviewer needs to double check?
I used the `.dark` class.. is that correct usage?
Made no issue as this is a minor upgrade to UI

## Why was this MR needed?
Clipboard buttons could obscure information in the merge info modal, this way its clean.

## Screenshots (if relevant)

From:
![image](/uploads/99269c9a314c593cb06239c27565b07c/image.png)

To:
![image](/uploads/7e278a5aaa8c57270e8a320cc270b5d8/image.png)


## 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
  - [ ] 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 it does - 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?
None, its a quick fix

See merge request !7145

CHANGELOG.md

@@ -28,6 +28,7 @@ Please view this file on the master branch, on stable branches it's out of date.
   - Show full status link on MR & commit pipelines
   - Fix documents and comments on Build API `scope`
   - Refactor email, use setter method instead AR callbacks for email attribute (Semyon Pupkov)
+  - Shortened merge request modal to let clipboard button not overlap
 
 ## 8.13.2
   - Fix builds dropdown overlapping bug !7124

app/assets/stylesheets/pages/merge_requests.scss

@@ -279,6 +279,10 @@
 #modal_merge_info .modal-dialog {
   width: 600px;
 
+  .dark {
+    margin-right: 40px;
+  }
+
   .btn-clipboard {
     @extend .pull-right;