Incorrect error locations for some syntax errors which refmt gets right

[hcarty]

Tested with esy and Reason 3.4.0.

• Wrong arrow in pattern matching case (-> instead of =>). refmt gets the error location correct.

let f = x =>
  switch x {
  | () -> /* Error should be at this arrow*/ ()
  }; /* Error shows up at the end of the file */

• Incomplete function definition. refmt says there's an error at the start of line 2, which is reasonable. vim-reasonml marks the l in let and simply has the message invalidCharacter.orComment.orString

let f = x =>

• let where it doesn't belong. Same error/issue as the previous example.

let f = () =>
  let

[hcarty]

I'll add more as I find them.