fix directive deep option test coverage

test/unit/specs/directive_spec.js

@@ -16,7 +16,7 @@ describe('Directive', function () {
     vm = new Vue({
       data:{
         a:1,
-        b: { c: 2 }
+        b: { c: { d: 2 }}
       },
       filters: {
         test: function (v) {
@@ -154,7 +154,7 @@ describe('Directive', function () {
     var d = new Directive('test', el, vm, {
       expression: 'b'
     }, def)
-    vm.b.c = 3
+    vm.b.c.d = 3
     nextTick(function () {
       expect(def.update.calls.count()).toBe(2)
       done()