Convert open.vim to unix line endings.

Hello. Thanks for your fix to issue #15. However, unfortunately, it looks as if some <CR> line endings have crept into autoload/gtfo/open.vim, which causes vim to see it as a DOS-formatted file, and it doesn't load correctly on OS X.

See http://stackoverflow.com/a/13978862/27641 for more information on the problem.

Can you fix the file format so it's UNIX-based? That should ensure (according to SO) maximum cross-platform compatibility. Here's a pull request that does that.