Update documentation to be consistent with testing frameworks and fix typos

The [description in NPM](https://npmjs.org/package/grunt-saucelabs) was out of date in that it did not mention Mocha or YUI. I updated this, plus fixed a few related inconsistencies:
- adding mocha/yui/qunit to the search terms for the npm module
- updated references to QUnit to use the same case
- fixed typos