Fixed styling of commit box in new MR

## What does this MR do?

Fixes an issue that caused the new merge request commit box to go all funny styled.

## What are the relevant issue numbers?

#18781 

## Screenshots (if relevant)

![Screen_Shot_2016-06-17_at_14.08.44](/uploads/b1e34b0c6bf67adc1be8748306e20b06/Screen_Shot_2016-06-17_at_14.08.44.png)

See merge request !4747