Added menuWidth to the _setOption function.

Author: mlh758

src/jquery.multiselect.js

@@ -729,6 +729,7 @@
           menu.find('ul').last().height(parseInt(value, 10));
           break;
         case 'minWidth':
+        case 'menuWidth':
           this.options[key] = parseInt(value, 10);
           this._setButtonWidth();
           this._setMenuWidth();