Source and target branch names swapped in UI merge conflict commit message

Summary

The source and target branch names are wrong in the auto generated commit message while resolving a merge conflict in Gitlab.

This can make for a very stressful situation.

Steps to reproduce

Resolve a merge conflict online while on the merge request screen.

Gitlab Version

Using self hosted GitLab Enterprise Edition 10.6.4-ee

What is the current bug behavior?

When handling merge conflicts via Gitlab the auto-generated commit message is wrong. The source and target branches are swapped in the current commit message.

Merge branch 'master' into 'dev'

What is the expected correct behavior?

Merge branch 'dev' into 'master'