fix: ignore branch merges with newlines

[marionebl]

• closes Commit messages in the format "Merge branch ..." fail linting #210

[dabit1gamma]

Hi! I'm sorry to say that It is not working properly. In this case, for example, it is not working:

Merge branch 'master' of https://github.com/xxx/xxx
#
# It looks like you may be committing a merge.
# If this is not correct, please remove the file
#	.git/MERGE_HEAD
# and try again.


# Please enter the commit message for your changes. Lines starting
# with '#' will be ignored, and an empty message aborts the commit.
#
# On branch master
# Your branch and 'origin/master' have diverged,
# and have 2 and 1 different commits each, respectively.
#   (use "git pull" to merge the remote branch into yours)
#
# All conflicts fixed but you are still merging.
#
# Changes to be committed:
#	modified:   config/locale/en.po
#	modified:   config/locale/es.po
#	modified:   config/locale/messages.pot
#

`