Quoted ES6 Getters/Setters Transpiled to Unquoted

```js
class Foo extends HTMLElement {
get 'foobar'() { return 'foobar'; }

attachedCallback() {
this.addEventListener('click', () => {
console.log(this['foobar']);
}, false);
}
}
window['Foo'] = Foo;
```

The transpiled getter for `foobar` is not properly quoted.