Do not build broken doc test. (#267)

This doctest cannot build successfully in recent toolchains because
the function is inaccessible to it. Since it is a non-public API,
not much is lost by disabling the doctest.

Author: briansmith

src/aes_hash.rs

@@ -34,7 +34,7 @@ impl AHasher {
     ///
     /// # Example
     ///
-    /// ```
+    /// ```no_build
     /// use std::hash::Hasher;
     /// use ahash::AHasher;
     ///