chore(modal): change to $uibUnscheduledDestruction

- Change to `$uibUnscheduledDestruction` as per comment in #4097

Author: wesleycho

Diff for: src/modal/docs/readme.md

@@ -35,7 +35,7 @@ In addition the scope associated with modal's content is augmented with 2 method
 
 Those methods make it easy to close a modal window without a need to create a dedicated controller.
 
-If the $scope is destroyed via unexpected mechanism, such as it being passed in the modal options and a $route/$state transition occurs, the modal will be dismissed with the value `$uibModal`.
+If the $scope is destroyed via unexpected mechanism, such as it being passed in the modal options and a $route/$state transition occurs, the modal will be dismissed with the value `$uibUnscheduledDestruction`.
 
 Finally, a `modal.closing` event is broadcast to the modal scope before the modal closes.  If the listener calls 
 preventDefault on the event, then the modal will remain open.  The $close and $dismiss methods return true if the 

Diff for: src/modal/modal.js

@@ -528,7 +528,7 @@ angular.module('ui.bootstrap.modal', [])
 
               modalScope.$on('$destroy', function() {
                 if (!modalScope.$$uibDestructionScheduled) {
-                  modalScope.$dismiss('$uibModal');
+                  modalScope.$dismiss('$uibUnscheduledDestruction');
                 }
               });