Fix references to non-existent `.rustup` directory.
Fix references to non-existent `.rustup` directory.

This should be reverted when #537 is fixed.

rust-lang/rustup,theindigamer/rustup.rs,theindigamer/rustup.rs,Boddlnagg/rustup.rs,rust-lang/rustup,nodakai/rustup.rs,polonez/rustup.rs,nodakai/rustup.rs,polonez/rustup.rs,theindigamer/rustup.rs,inejge/rustup.rs,inejge/rustup.rs,Boddlnagg/rustup.rs,Boddlnagg/rustup.rs,rust-lang/rustup,inejge/rustup.rs,Boddlnagg/rustup.rs,polonez/rustup.rs,polonez/rustup.rs,polonez/rustup.rs,inejge/rustup.rs,theindigamer/rustup.rs,nodakai/rustup.rs,rust-lang/rustup,nodakai/rustup.rs,inejge/rustup.rs,theindigamer/rustup.rs,nodakai/rustup.rs,rust-lang/rustup,Boddlnagg/rustup.rs