Add `grunt clean`
Add `grunt clean`

- Removes the `app.js` file from the build directory in the default task (build uses app.min.js)
- Removes the build/ and bin/ directories when the task is run by itself

whitef0x0/Necromunda,wellesleywatson/info3180-lab4,yahsharahla/info3180-lab4,aziegler/boilerplate,philipcressler/personal-game,melonjs/boilerplate,whitef0x0/Necromunda,philipcressler/personal-game,blipjoy/boilerplate,yahsharahla/info3180-lab4,blipjoy/boilerplate,Samorae-Campbell/info3180-lab4,aziegler/boilerplate,jjhanso/aub-game-tutorial,Samorae-Campbell/info3180-lab4,aziegler/ggj16Lille,cdwuestner/capstone,jjhanso/aub-game-tutorial,wellesleywatson/info3180-lab4,melonjs/boilerplate,cdwuestner/capstone,aziegler/ggj16Lille