Remove requirement to globally install Grunt

[evanplaice]

If grunt is already included in package.json what's the point of installing it globally? It would make a lot more sense to run it as a NPM script.

package.json

...
  "license": "MIT",
  "scripts": {
    "uglify": "grunt uglify"
  }, 
  "devDependencies": {
    "grunt": "^0.4.5",
...

Note: This'll make the project more self-contained and avoid environment-level version differences between users. For a better explanation of the reasoning behind my suggestion, I suggest taking a look at The Twelve Factor App - II. Dependencies