code: function ( files ) {
          var me = this;
          files = files || [ ];
  
          return me.normalizeEntries( files ).filter( function ( entry ) {
            return entry.changed;
          } ).map( function ( entry ) {
            return entry.key;
          } );
        }
docs: Return the list o the files that changed compared
  against the ones stored in the cache
  
  @method getUpdated
  @param files {Array} the array of files to compare against the ones in the cache
  @returns {Array}