broken link in hyper::upgrade documentation

[miquels]

in https://docs.rs/hyper/0.12.6/hyper/upgrade/index.html it says:

See this example showing how upgrades work with both Clients and Servers.

That link is broken. It should probably be https://github.com/hyperium/hyper/blob/master/examples/upgrades.rs instead.

[seanmonstar]

Doh! Thanks for the report!