fix(mdAutocomplete): Fix scope watch bug.

Commit 8849213 introduced a scope
watching bug cauinsg the autocomplete to no longer update it's list
of items as you scrolled (since it re-uses DOM elements). Fix by
swapping nextTick to be inside the watch statement.

Fixes angular#4713. Closes angular#4715.

src/components/autocomplete/js/autocompleteParentScopeDirective.js

@@ -10,7 +10,7 @@ function MdAutocompleteItemScopeDirective($compile, $mdUtil) {
   };
 
   function postLink(scope, element, attr) {
-    var ctrl     = scope.$mdAutocompleteCtrl;
+    var ctrl = scope.$mdAutocompleteCtrl;
     var newScope = ctrl.parent.$new();
     var itemName = ctrl.itemName;
 
@@ -32,10 +32,13 @@ function MdAutocompleteItemScopeDirective($compile, $mdUtil) {
      * @param variable
      * @param alias
      */
-    function watchVariable (variable, alias) {
-      $mdUtil.nextTick(function () {
-        newScope[alias] = scope[variable];
-        scope.$watch(variable, function (value) { newScope[alias] = value; });
+    function watchVariable(variable, alias) {
+      newScope[alias] = scope[variable];
+
+      scope.$watch(variable, function(value) {
+        $mdUtil.nextTick(function() {
+          newScope[alias] = value;
+        });
       });
     }
   }