build.rs: fix formatting

.radicle/native.yaml runs "cargo fmt --check" and that fails without
this change.

Signed-off-by: Lars Wirzenius <liw@liw.fi>

build.rs

@@ -1,5 +1,5 @@
-use std::process::Command;
 use std::env;
+use std::process::Command;
 
 fn main() {
     // Set a build-time `GIT_HEAD` env var which includes the commit id;