Error when trying to format file with some UTF-8 characters in string literal

[pmk1c]

RuFo 0.7.0
Ruby 2.4.6

When I try to format a file with the following string with typographic quotation marks in it, RuFo gives me an error:

Error: Failed with exit code: 1 - unknown error

"“”"

Edit: The same goes for "–" (which is a en dash not a minus). So this may be a problem with UTF-8 mutibyte characters.

[pmk1c]

This seems to be a problem with the vscode-ruby integration and not with RuFo itself.