adding `.jslintrc` file

lets tell jslint that we are running node, so we can remove all the
globals and all the “”Use the function form of "use strict" [issues](https://scrutinizer-ci.com/g/tcarlsen/atom-message-panel/inspec
tions/7d995b42-cd51-49c3-8ebc-22a8d88133ea/issues/)