Fix missing flash messages on service edit page

## What does this MR do?

This MR fixes missing post-update flash notifications for service edit page. Bug was introduced in https://gitlab.com/gitlab-org/gitlab-ce/commit/76aad9b76ed756ca9ba2cbcdb399c815e542b3ae#3ca7aff54d2814b971a98a7bf2837e07ab3dfa04_21_20 and caused by passing `notice: Successfully updated.` to path helper instead of passing it to `redirect_to` due to wrong parenthesis placement.

## Why was this MR needed?

While adding HipChat integration I noticed that no messages are being displayed after clicking on "Save changes" button. I looked into code and observed that there is a code for these messages which once worked but doesn't work anymore. It's a regression which should be fixed.

## Screenshots (if relevant)

![image](/uploads/32b851e5bdc2a6438f35061473db9650/image.png)

## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- Tests
  - [x] Added for this feature/bug
  - [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)

See merge request !6195