Fix groups sort dropdown alignment

## What does this MR do?
Changes the dropdown located on the [explore groups page](https://gitlab.com/explore/groups) from left aligned to right aligned.

## Are there points in the code the reviewer needs to double check?
Shouldn't be

## Why was this MR needed?
Keeps the UI consistent for dropdowns as they are right aligned on other pages

## What are the relevant issue numbers?
Closes #21296

## Screenshots (if relevant)

Before:
![Screen_Shot_2016-08-23_at_11.21.01_AM](/uploads/9723d0166b80dcb8d7b0228063e39a77/Screen_Shot_2016-08-23_at_11.21.01_AM.png)

After:
![Screen_Shot_2016-08-23_at_11.20.52_AM](/uploads/5a55a72c10909142d02a23710736a93f/Screen_Shot_2016-08-23_at_11.20.52_AM.png)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [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 !5963