Replaced "npm remove" with "npm uninstall"

[FAQ page](http://gruntjs.com/frequently-asked-questions) tells to use `npm remove [GRUNT_PLUGIN] --save-dev` to uninstall unwanted plugins, while [correct command](https://www.npmjs.org/doc/cli/npm-uninstall.html) is `npm uninstall [GRUNT_PLUGIN] --save-dev`. While `npm remove` still work it is an alias.