Build: Upgrade to grunt-contrib-jshint 0.7.1 and squash subtasks

grunt-contrib-jshint 0.7.1 allows the jshintrc option to be set to true to have
it read the appropriate config file based on the file being checked. The only
place where we can’t use it is the check for dist/jquery.js that has the onevar
option removed.

Fixes #14504