Merge branch 'add-sub-nav-active-color' into 'master'

Add blue back to sub nav active

## What does this MR do?
Adds blue color back active sub nav tab

## Screenshots (if relevant)
![Screen_Shot_2016-11-29_at_10.00.55_AM](/uploads/b968fce60d8e25e7f0769f6fb045291c/Screen_Shot_2016-11-29_at_10.00.55_AM.png)

## Does this MR meet the acceptance criteria?

- [ ] [Changelog entry](https://docs.gitlab.com/ce/development/changelog.html) 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?
https://gitlab.com/gitlab-org/gitlab-ce/issues/24149

See merge request !7829

app/assets/stylesheets/framework/nav.scss

@@ -94,6 +94,7 @@
 
       &.active a {
         border-bottom: none;
+        color: $link-underline-blue;
       }
 
       a {
@@ -103,7 +104,6 @@
         &:hover,
         &:active,
         &:focus {
-          color: $black;
           border-bottom: none;
         }
       }