fix(datepicker): assign initDate correctly to the controller

Closes #5541

Author: Foxandxss

src/datepicker/datepicker.js

@@ -130,15 +130,15 @@ angular.module('ui.bootstrap.datepicker', ['ui.bootstrap.dateparser', 'ui.bootst
           break;
         case 'initDate':
           if ($scope.datepickerOptions.initDate) {
-            this.activeDate = dateParser.fromTimezone($scope.datepickerOptions.initDate, ngModelOptions.timezone) || new Date();
+            self.activeDate = dateParser.fromTimezone($scope.datepickerOptions.initDate, ngModelOptions.timezone) || new Date();
             $scope.$watch(function() { return $scope.datepickerOptions.initDate; }, function(initDate) {
               if (initDate && (ngModelCtrl.$isEmpty(ngModelCtrl.$modelValue) || ngModelCtrl.$invalid)) {
                 self.activeDate = dateParser.fromTimezone(initDate, ngModelOptions.timezone);
                 self.refreshView();
               }
             });
           } else {
-            this.activeDate = new Date();
+            self.activeDate = new Date();
           }
       }
     });