Copy .jshintrc from Parsoid.

Ib78b8353d01156b29ff9cda65865dccc3a3e402d wasn't enough; jshint also
needs to be put in 'node mode'.

In addition, we need to add a few `"use strict";` statements to satisfy
jshint.  (It's also good hygiene in any case.)

Change-Id: Id7178fe99b2d620d4905d294d04082c0e5f5406d