Add mix_test_watch v1.1.0 as dev dep

[joeljuca]

Hello!

Please consider this PR as a suggestion to add mix_test_watch as a dev dependency. It's good to have a lightweight test watcher running while you work on something in the library. :)

[joeljuca]

I'm not totally sure if it would include mix_test_watch in the releases, though. I hope not – but I saw other dev/test-only projects like benchee, ex_doc, jason, etc., so I thought it wouldn't affect releases.

[warmwaffles]

I'm not a fan of mix_test_watch I can accomplish the same thing with https://github.com/eradman/entr. I also don't think this project has enough of active development to find it useful.

http://eradman.com/entrproject/

[joeljuca]

Sounds fair. I also heard about Ruby's rerun yesterday, which apparently works similarly to entr.

[warmwaffles]

entr is pretty sweet, I use it for other projects and it works well 99% of the time.