docs(upgrade): update 0.12.x links of examples

Author: seanmonstar

src/client/mod.rs

@@ -24,7 +24,7 @@
 //! ## Example
 //!
 //! For a small example program simply fetching a URL, take a look at the
-//! [full client example](https://github.com/hyperium/hyper/blob/master/examples/client.rs).
+//! [full client example](https://github.com/hyperium/hyper/blob/0.12.x/examples/client.rs).
 //!
 //! ```
 //! extern crate hyper;

src/upgrade.rs

@@ -3,7 +3,7 @@
 //! See [this example][example] showing how upgrades work with both
 //! Clients and Servers.
 //!
-//! [example]: https://github.com/hyperium/hyper/blob/master/examples/upgrades.rs
+//! [example]: https://github.com/hyperium/hyper/blob/0.12.x/examples/upgrades.rs
 
 use std::any::TypeId;
 use std::error::Error as StdError;