Clicking on std::rc's [src] link redirects to `.../alloc/rc/undefined`

[huonw]

The [src] link on http://doc.rust-lang.org/master/std/rc/index.html points to http://doc.rust-lang.org/master/alloc/rc/?gotosrc=1815 but that redirects to http://doc.rust-lang.org/master/alloc/rc/undefined

[alexcrichton]

Closing as a dupe of #15309