Bump favcount.js to v1.5.0

We fixed a CORS issue in https://github.com/discourse/discourse/commit/7b20079d852dfef62f8afca2949c9a2f9c43d49f :sparkles:, but I'm bumping the version here as well to [match upstream](https://github.com/chrishunt/favcount/commit/7687447096444c4f234ca500fa983c20bfca4372).

Thank you!

cc @eviltrout https://github.com/chrishunt/favcount/pull/8