Fixes compilation errors with HashMap and HashSet

As of rust-lang/rust commit e84e7a00ddec76570bbaa9afea385d544f616814
HashMap and HashSet can be found at std::collections::{HashMap,HashSet}
and are no longer under std::collections::hashmap.

Signed-off-by: zachwick <zach@zachwick.com>
Merge pull request #4 from ZachWick/master

Fixes compilation errors with HashMap and HashSet