Don't call gsub on safe strings

Calling #gsub on a string that was previously marked as #html_safe will lead to unexpected behavior. E. g. backreferences to captured groups ($1, $2) will be nil even if the group was matched.

There is no universal workaround available since you can't expect #html_safe strings Show archive.org snapshot to still be safe after using gsub on them.

You can, however, fix the $1 gsub behavior on html_safe strings.