test(contrib): enforce valid commit messages

This unit test intentionally forces the user to adhere to our
commit style guidelines. This helps us ensure that every commit
coming into Deis is a valid commit.

for more information on the change to the commit line length, see
https://github.com/blog/926-shiny-new-commit-styles

closes #1266

Note that for this commit, I moved the date before July 8th just to make sure that Travis fails.