Assure a change of the WEB_ROOT value in the Gruntfile works fine

[hhzl]

In the Gruntfile.js the value for the input directory may be changed and the tasks work fine. Make sure this is as well possible for a change of WEB_ROOT.

      var INPUT_DIR = 'data',
      WEB_ROOT = 'public',
      BUILD_DIR = path.join(WEB_ROOT,'js'),
      DIST_DIR = 'dist';