Update jshintrc to support ES6 and not warn about unused parameters.
Review Request #8277 — Created July 11, 2016 and submitted
This gets jshint set up to support validating ES6, for some upcoming work happening in Djblets. It also tweaks the unused variable option to only warn about actual variables and not function parameters (which we often want to declare but not use, such as in a base class).
Ran jshint against some upcoming code. Saw that it no longer complained
about the unused function parameters in a base class, and that it had no
problem with the new ES6 code.