Remove #[deny(warnings)]

The library currently does not currently build anymore, because upstream
libraries have added new deprecation warnings. A deprecation warning
should not break compilation though.

Author: dbrgn

src/lib.rs

@@ -11,7 +11,6 @@
 //! [0]: https://crates.io/keywords/embedded-hal
 
 #![deny(missing_docs)]
-#![deny(warnings)]
 
 extern crate cast;
 extern crate embedded_hal as hal;