Fix OSX-specific Icon\r rule

Rule for the file `Icon\r` of MacOSX is broken since https://github.com/github/gitignore/commit/174c45e796b57d79ac1b8a400559d6b7a272a4a5 .
It must ends with two `\r` (Carriage return).

Current rule matches all `icon` folder/file, not `Icon\r` file.