GitLab

Aligns create merge request button vertically

## What does this MR do?

Based on https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4644#note_12507178 I have vertically aligned the button correctly.

## Screenshots (if relevant)

Here is my awesome screenshot to show it is centered vertically 

![Screen_Shot_2016-06-17_at_10.17.19](/uploads/e7bf5bcc5b254ed4db376c16460d79a5/Screen_Shot_2016-06-17_at_10.17.19.png)

See merge request !4733