Added async/await example (#1338)

Added example of using async/await on functions that are using Promises under the hood.

Author: karatekaneen

docs/guides/getting-started.md

@@ -121,7 +121,7 @@ it('will time out', done => {
   })
 })
 
-// the two following tests will work as expected
+// the three following tests will work as expected
 it('will catch the error using done', done => {
   Vue.config.errorHandler = done
   Vue.nextTick(() => {
@@ -135,6 +135,11 @@ it('will catch the error using a promise', () => {
     expect(true).toBe(false)
   })
 })
+
+it('will catch the error using async/await', async () => {
+  await Vue.nextTick()
+  expect(true).toBe(false)
+})
 ```
 
 ### What's Next