Enable doc testing of Uuid::new_v4 example

The doc testing of the Uuid::new_v4() example was currently disabled,
but after fixing the errors in df0dc49 the test is now working again.

src/lib.rs

@@ -87,15 +87,15 @@
 //!
 //! To create a new random (V4) UUID and print it out in hexadecimal form:
 //!
-//! ```ignore,rust
+//! ```rust
 //! // Note that this requires the `v4` feature enabled in the uuid crate.
 //!
 //! use uuid::Uuid;
 //!
 //! fn main() {
 //! #    #[cfg(feature = "v4")] {
 //!      let my_uuid = Uuid::new_v4();
-//!      println!("{}", my_uuid);
+//!      println!("{}", my_uuid)
 //! #    }
 //! }
 //! ```