Patch 5

Yesterday I forgot to add the reject in the ready function:
```js
localForage._ready.then(resolve, reject);
```
I also decided to add reject in other drivers as well since it was missing too !
There is one last promise in the websql driver without a reject: https://github.com/mozilla/localForage/blob/master/src/drivers/websql.js#L50
I wasn't sure how to do it (reject the `db.transaction` or the `t.executeSql` ? both ?), I'll let you do it.