New git hook script name

[hadrizi]

https://github.com/rust-lang/rustc-dev-guide/blob/master/src/building/suggested.md contains broken link https://github.com/rust-lang/rust/blob/master/src/etc/pre-commit.sh. This script is now called pre-push.sh