Arrow functions: Signature not tokenized the same way as for functions

Tokenize this:

``` typescript
 return this.travelWorld((cell: Cell) => {
 cell.live = Math.random() < this.initialLifeProbability;
 return cell;
 });
```

Note that `cell: Cell` is a single token (scope `block body decl declaration meta method object ts`).
It would be great if it can follow the tokenization for functions
