Fix "Missing initializer" error with using option in positioning

Author: alex-solovyev

ui/position.js

@@ -285,7 +285,7 @@ $.fn.position = function( options ) {
 		if ( options.using ) {
 
 			// Adds feedback as second argument to using callback, if present
-			using = function( props ) {
+			var using = function( props ) {
 				var left = targetOffset.left - position.left,
 					right = left + targetWidth - elemWidth,
 					top = targetOffset.top - position.top,