In 6f08fdd26, I left in a typo after copying from my `~/.nixpkgs/config`.
I would normally test this out locally, but I'm fixing up my conf locally,
and, in the interest of not forgetting to push this change up, made the edit
through GitHub's UI.
Oops.
This updates macvim to 7.4.648. This also fixes the build, which was broken when I set the default Ruby version to 2.2.2 (one of the symbols was renamed).
MacVim's maintenance has stagnated, so this moves `macvim` to a new maintainer.
Additionally, the `-headerpad_max_install_names` linker flag is passed to
prevent problems when setting the rpaths.
