Highlight on multiline string syntax error is wrong

[Ruud van Asseldonk]

Consider the following invalid input:

{
  ---
  foo
  ---
}

It triggers the following error message:

Parse error at line 2:

  ---
  ^~~~~~~~~~~~~~~
Error: Parse error in statement: expected import, return, assignment, block, or put.

The highlight of ~~~ should not extend that long; the end of line inside the multiline string should be taken into account.