Change update function to use decryption rather than encryption. (tkaitchuck#173)

* Change update function to use decryption rather than encryption

---------

Signed-off-by: Tom Kaitchuck <tom.kaitchuck@emc.com>

Author: tkaitchuck

smhasher/ahash-cbindings/src/lib.rs

@@ -1,5 +1,3 @@
-#![feature(build_hasher_simple_hash_one)]
-
 use ahash::*;
 use core::slice;
 use std::hash::{BuildHasher};