Instead of specifying the `grunt` command here, I think it would be better to put it in `package.json` and use the convention that `npm test` runs the tests.

When the language is configured to be `node_js`, travis automatically runs `npm install` and `npm test`... cf [here](http://about.travis-ci.org/docs/user/languages/javascript-with-nodejs/). So, if the test command to execute is correctly configured in the `package.json`, then there should be no need to specify it here, and we could also remove the `npm install` command from here.