Run rustfmt.

examples/stm32f7/build.rs

@@ -1,7 +1,8 @@
 //! adapted from https://github.com/stm32-rs/stm32f7xx-hal/blob/master/build.rs
 use std::env;
 use std::fs::File;
-use std::io::{self, prelude::*};
+use std::io::prelude::*;
+use std::io::{self};
 use std::path::PathBuf;
 
 #[derive(Debug)]