Embedded javascript ``this`` in fat-arrow function should not compile to `_this`

This 1.10.0 code:

``` coffee
() => 
  foo = this
  bar = `this`
  return
```

Compiles to:

``` js
(function(_this) {
  return (function() {
    var bar, foo;
    foo = _this;
    bar = _this;
  });
})(this);
```

Whereas I really expected it to compile to:

``` js
(function(_this) {
  return (function() {
    var bar, foo;
    foo = _this;
    bar = this;
  });
})(this);
```
