docs: improve parentComponent example (#963)

Author: eddyerburgh

docs/api/options.md

@@ -254,7 +254,7 @@ import Foo from './Foo.vue'
 const wrapper = shallowMount(Component, {
   parentComponent: Foo
 })
-expect(wrapper.vm.$parent.name).toBe('foo')
+expect(wrapper.vm.$parent.$options.name).toBe('foo')
 ```
 
 ## provide

docs/ja/api/options.md

@@ -222,7 +222,7 @@ import Foo from './Foo.vue'
 const wrapper = shallowMount(Component, {
   parentComponent: Foo
 })
-expect(wrapper.vm.$parent.name).toBe('foo')
+expect(wrapper.vm.$parent.$options.name).toBe('foo')
 ```
 
 ## provide

docs/ru/api/options.md

@@ -245,7 +245,7 @@ import Foo from './Foo.vue'
 const wrapper = shallowMount(Component, {
   parentComponent: Foo
 })
-expect(wrapper.vm.$parent.name).toBe('foo')
+expect(wrapper.vm.$parent.$options.name).toBe('foo')
 ```
 
 ## provide

docs/zh/api/options.md

@@ -197,7 +197,7 @@ import Foo from './Foo.vue'
 const wrapper = shallowMount(Component, {
   parentComponent: Foo
 })
-expect(wrapper.vm.$parent.name).toBe('foo')
+expect(wrapper.vm.$parent.$options.name).toBe('foo')
 ```
 
 ## provide