fix(uiSelectSort): update model on sort completion

Previously when order of selected items was changed, the ngModel value was not updated. 

This commit causes the model to be invalidated after a change to the order, triggering a refresh.

Fixes #974 & Closes #1036

src/uiSelectSortDirective.js

@@ -1,12 +1,15 @@
 // Make multiple matches sortable
 uis.directive('uiSelectSort', ['$timeout', 'uiSelectConfig', 'uiSelectMinErr', function($timeout, uiSelectConfig, uiSelectMinErr) {
   return {
-    require: '^^uiSelect',
-    link: function(scope, element, attrs, $select) {
+    require: ['^^uiSelect', '^ngModel'],
+    link: function(scope, element, attrs, ctrls) {
       if (scope[attrs.uiSelectSort] === null) {
         throw uiSelectMinErr('sort', 'Expected a list to sort');
       }
 
+      var $select = ctrls[0];
+      var $ngModel = ctrls[1];
+
       var options = angular.extend({
           axis: 'horizontal'
         },
@@ -99,6 +102,8 @@ uis.directive('uiSelectSort', ['$timeout', 'uiSelectConfig', 'uiSelectMinErr', f
 
         move.apply(theList, [droppedItemIndex, newIndex]);
 
+        $ngModel.$setViewValue(Date.now());
+
         scope.$apply(function() {
           scope.$emit('uiSelectSort:change', {
             array: theList,