Failing test for multiple kwargs in blocks

Hey there!

This code:

```ruby
Proc.new{ |kw: :val, kw2: :val2 | [kw,kw2] }[{}]
```

raises a `not yet` error when run through the Ruby20Parser. I added a failing test case. I'm sorry if this is already on your radar (as indicated by this error being raised?) just didn't see any obvious other way to handle it and a failing test case always seems useful.