`abstract type` and `primitive type` are highlighted oddly

[ararslan]

Disclaimer: This issue mostly concerns the GitHub UI, which uses this repo for syntax recognition. I'm not sure whether this similarly applies to TextMate itself.

Consider the following:

mutable struct A end  # all red
abstract type B end   # purple abstract
primitive type C end  # purple primitive

These definitions were introduced in #15. It's not clear to me why abstract and primitive are showing in a different color than mutable. It would be nice for consistency if they matched.