Revert cargo-deb install back to use crates.io

Since `cargo-deb` has been updated on crates.io it is now
possible to just install it from crates.io and build Alacritty's
deb without having to rely on github.

README.md

@@ -56,7 +56,7 @@ Using `cargo deb`, you can create and install a deb file.
 ```sh
 git clone https://github.com/jwilm/alacritty.git
 cd alacritty
-cargo install --git https://github.com/mmstick/cargo-deb cargo-deb
+cargo install cargo-deb
 cargo deb --install
 ```