Bug: '-r' parameter does not work with scoped package

[BolkoSchreiber]

markdownlint -r @myScope/custom_rules_package . does not work.

error msg:

Cannot load custom rule @myScope/custom_rules_package: No such rule

workaround:
install scoped package locally and change cli call to

markdownlint -r node_modules/@myScope/custom_rules_package .

[DavidAnson]

Glancing at the code, I think tryResolvePath is incorrectly deciding this is a file path based on having a slash in it.