use nextTick with context in batcher

src/batcher.js

@@ -30,10 +30,7 @@ p.push = function (job) {
     this.has[job.id] = job
     if (!this.waiting) {
       this.waiting = true
-      var self = this
-      _.nextTick(function () {
-        self.flush()
-      })
+      _.nextTick(this.flush, this)
     }
   } else if (job.override) {
     var oldJob = this.has[job.id]

test/unit/specs/watcher_spec.js

@@ -109,11 +109,16 @@ describe('Watcher', function () {
 
   it('non-existent path, $add later', function (done) {
     var watcher = new Watcher(vm, 'd.e', spy)
+    var watcher2 = new Watcher(vm, 'b.e', spy)
     expect(watcher.value).toBeUndefined()
+    expect(watcher2.value).toBeUndefined()
     vm.$scope.$add('d', { e: 123 })
+    vm.b.$add('e', 234)
     nextTick(function () {
       expect(watcher.value).toBe(123)
+      expect(watcher2.value).toBe(234)
       expect(spy).toHaveBeenCalledWith(123, undefined)
+      expect(spy).toHaveBeenCalledWith(234, undefined)
       done()
     })
   })