Make push events have equal vertical spacing.

## What does this MR do?

Evens out the vertical space between lines in push events.

## Are there points in the code the reviewer needs to double check?

Not afaik. 

## Why was this MR needed?

UI consistency.

## What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/19517

## Screenshots (if relevant)

Before: 
![Screen_Shot_2016-08-26_at_5.23.33_PM](/uploads/78e7a89912ec504d598f9bfec2a83eea/Screen_Shot_2016-08-26_at_5.23.33_PM.png)
After: 
![Screen_Shot_2016-08-26_at_5.23.16_PM](/uploads/3fa3e0902ef76b1e9c82e052842cd0ee/Screen_Shot_2016-08-26_at_5.23.16_PM.png)




## Does this MR meet the acceptance criteria?

- [x] [CHANGELOG](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG) entry added
- [x] [Documentation created/updated](https://gitlab.com/gitlab-org/gitlab-ce/blob/master/doc/development/doc_styleguide.md)
- [x] API support added
- Tests
  - [ ] Added for this feature/bug
  - [ ] 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)

cc: @winniehell

See merge request !6055