Auto merge of #6404 - ehuss:fix-install-link, r=alexcrichton
Auto merge of #6404 - ehuss:fix-install-link, r=alexcrichton

Fix install link.

The new website broke the old links. They are setting up redirects (https://github.com/rust-lang/www.rust-lang.org/pull/597), but I figured may as well use the new location to avoid the redirect.

tshepang/cargo,rust-lang/cargo,nipunn1313/cargo,tsurai/cargo,rust-lang/cargo,nipunn1313/cargo,tshepang/cargo,rustyhorde/cargo,tsurai/cargo,tsurai/cargo,rustyhorde/cargo,vojtechkral/cargo,eminence/cargo,nipunn1313/cargo,vojtechkral/cargo,rust-lang/cargo,tsurai/cargo,eminence/cargo,nipunn1313/cargo,rustyhorde/cargo,eminence/cargo,vojtechkral/cargo,tshepang/cargo,rust-lang/cargo,tshepang/cargo,vojtechkral/cargo,rustyhorde/cargo,tsurai/cargo,eminence/cargo