Adjusted unit tests for Chrome 54 optimizations.
Adjusted unit tests for Chrome 54 optimizations.

Async / await optimizations in Chrome 54 makes us loose zone when awaiting already resolved promises.

Adjusted unit tests so that we test the important stuff:
1. We can have an async function that returns asynchronous promises and await the promise returned by that async function.
2. We can await sub transactions.

jimmywarting/Dexie.js,jimmywarting/Dexie.js,chrahunt/Dexie.js,jimmywarting/Dexie.js,jimmywarting/Dexie.js,dfahlander/Dexie.js,chrahunt/Dexie.js,dfahlander/Dexie.js,dfahlander/Dexie.js,chrahunt/Dexie.js,chrahunt/Dexie.js,dfahlander/Dexie.js