Improve parsing and error message for curried function missing parens

[lukewilliamboswell]

The following gives a cryptic error message. The curried function should include parens, but they are missing. This is difficult for users to spot unless they are already very familiar with the syntax (in which case they may never see this error).

module [main]

main : U8 -> _ -> Task U8 _

# should be, works ok
# main : U8 -> (_ -> Task U8 _)

$ roc check example.roc
── SYNTAX PROBLEM in example.roc ───────────────────────────────────────────────

I got stuck here:

1│  module [main]
2│
3│  main : U8 -> _ -> Task U8 _
                  ^

Whatever I am running into is confusing me a lot! Normally I can give
fairly specific hints, but something is really tripping me up this