[fix] use smooth icon (again)

I found the icon set via b4winckler#44

There are two blog posts from the (original?) author:
https://girlintroverted.wordpress.com/2014/08/15/filedoc-icons-for-macvim/
https://girlintroverted.wordpress.com/2014/08/26/macvim-doc-icons-redux-howto/

But yet, I simply cpoied the icons directly into the icns dir.