Merge from upstream and update dependencies

Merged from gruntjs/grunt-contrib-qunit, and updated version to match (0.3.0). Also updated unique istanbul dependencies (rimraf, istanbul, and grunt-lib-phantomjs-istanbul). As such, this shouldn't be merged until after the similar pull request on grunt-lib-phantomjs-istanbul (https://github.com/asciidisco/grunt-lib-phantomjs-istanbul/pull/1) has been merged in, bumping that version to 0.4.0.