Fix greedy shortened_filename replace
Fix greedy shortened_filename replace

Uses sub instead of gsub to avoid replacing file paths that include the root, such as the "app" in "application" when the source directory is "/app".

Example of issue: https://gist.github.com/akamike/393bede2b89645b946c8d95ac4f5bcf9
colszowka/simplecov-html,colszowka/simplecov-html,colszowka/simplecov-html