docs: replace shallow by shallowMount (#15)

Author: aantipov

README.md

@@ -21,12 +21,12 @@ You need to tell Jest to use the serializer. Add this to your Jest config:
 And your snapshot tests will be pretty printed 💅
 
 ```js
-import { shallow } from '@vue/test-utils'
+import { shallowMount } from '@vue/test-utils'
 import Basic from './Basic.vue'
 
 describe('Basic.vue', () => {
   it('renders correctly', () => {
-    const wrapper = shallow(Basic)
+    const wrapper = shallowMount(Basic)
     expect(wrapper).toMatchSnapshot()
   })
 })