[Fixes #9] Fix Zalgo
[Fixes #9] Fix Zalgo

Ensure scheduled callbacks are never invoked synchronously.

Prior to this PR:

In environments with `window`

```js
let x = 0
scheduleWork(() => x++);
x++;
// x === 1;
```

In environments without `window`.

```js
let x = 0
scheduleWork(() => x++);
x++;
// x === 2;
```

WIth this PR, we always get:

```js
let x = 0
scheduleWork(() => x++);
x++;
// x === 1;
```
asakusuma/ember-spaniel,asakusuma/ember-spaniel