Actually forbid unsafe code

The code of this crate is 100% safe Rust, but the lint setting in the
README is not accurate.

Author: mbrubeck

README.md

@@ -47,7 +47,7 @@ $ cargo add async-h1
 ```
 
 ## Safety
-This crate uses ``#![deny(unsafe_code)]`` to ensure everything is implemented in
+This crate uses ``#![forbid(unsafe_code)]`` to ensure everything is implemented in
 100% Safe Rust.
 
 ## Contributing

src/lib.rs

@@ -91,7 +91,7 @@
 //! }
 //! ```
 
-// #![forbid(unsafe_code, rust_2018_idioms)]
+#![forbid(unsafe_code, rust_2018_idioms)]
 #![deny(missing_debug_implementations, nonstandard_style)]
 #![warn(missing_docs, missing_doc_code_examples, unreachable_pub)]
 #![cfg_attr(test, deny(warnings))]