Coauthors are not appended properly when using `git commit -m ""`

[ryanjwessel]

It seems like coauthors are prepended to the commit message when the author uses git commit -m "message", rather than using the vim editor by only entering git commit.

# with git commit -m
Co-authors: Name1, Name2
Intended commit title

# with git commit
Intended commit title

Co-authors: Name1, Name2

[ryanjwessel]

This was addressed in 4bc02ef