parser: comment not allowed inside lists

[i4ki]

The parser complain in the code below:

tests = (
      # oops
     some
     list
)

The parser is right regarding our specification, but I think we need to improve it: https://github.com/NeowayLabs/nash/blob/master/spec.ebnf#L75

[katcipis]

I tried to do this these days and got surprised it did not work, it would definitely be good :+1: