Fix inconsistent options dropdown caret on mobile viewports

## What does this MR do?
Change the options dropdown caret from left aligned to right aligned (only visible on mobile viewports)

## Are there points in the code the reviewer needs to double check?
Check if there are any other dropdowns that have left aligned carets

## Why was this MR needed?
Resolve UI inconsistency as some dropdown carets were already right aligned

## Screenshots (if relevant)
Before:
![Simulator_Screen_Shot_Sep_15__2016__11.54.55_AM](/uploads/767d9344db4973af5a5368d5149144cc/Simulator_Screen_Shot_Sep_15__2016__11.54.55_AM.png)

After:
![Simulator_Screen_Shot_Sep_15__2016__11.54.09_AM](/uploads/882614cb9c5f85bf44e118cd7c74fcef/Simulator_Screen_Shot_Sep_15__2016__11.54.09_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 [merge request performance guides](http://docs.gitlab.com/ce/development/merge_request_performance_guidelines.html)
- [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)

## What are the relevant issue numbers?
Closes #22086

See merge request !6372