Support new merge commit format for GitLab v10.0.0+

Merge commit message format is changed since v10.0.0.

So gitlab_awesome_release doesn't work 😢

Before

Merge branch 'feature/fresh' into 'develop'

Add fresh

See merge request !7

After

Merge branch 'feature/alamode' into 'develop'

Add a_la_mode

See merge request sue445/gitlab_example!28

Detail

• https://gitlab.com/gitlab-org/gitlab-ce/blob/master/CHANGELOG.md#1000-2017-09-22

Close #24