Merge request widget checkboxes are not aligned on mobile

Summary

Merge request widget can have 2 checkboxes: Delete source branch and Squash commits. They are not aligned well on small screen resolutions.

Steps to reproduce

• open merge request with multiple commits
• open MR
• enable device toolbar in Chrome browser
• select iPhone 6/7/8 (375px wide)
• have a look at checkboxes next to Merge button

What is the current bug behavior?

Delete source branch is aligned left and Squash commits checkbox is aligned center.

What is the expected correct behavior?

Both checkboxes should have consistent alignment

Relevant logs and/or screenshots