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

[aeschli]

Tokenize this:

            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

[sheetalkamat]

Fixed by #257