Added eslint support

[sadasant]

No description provided.

[coveralls]

Coverage remained the same at 86.029% when pulling 86d2cb2 on feature/eslint into 768e4dd on master.

[sadasant]

Proof that it fails if the changed files have eslint errors: https://travis-ci.org/smartprocure/futil-js/builds/202384532

You can try yourself individual pieces of the code to see the diff files. For example, the following line will show you the files changed from master in your current branch.

LIST=$(git diff-index --name-only origin/master | grep .*\\.js | grep -v json | grep -v eslint | tr '\n' ' '); echo $LIST