visually separate conditional imports in 'os_str.rs'

Author: JOE1994

src/shims/os_str.rs

@@ -2,11 +2,12 @@ use std::borrow::Cow;
 use std::convert::TryFrom;
 use std::ffi::{OsStr, OsString};
 use std::iter;
+use std::path::{Path, PathBuf};
+
 #[cfg(unix)]
 use std::os::unix::ffi::{OsStrExt, OsStringExt};
 #[cfg(windows)]
 use std::os::windows::ffi::{OsStrExt, OsStringExt};
-use std::path::{Path, PathBuf};
 
 use rustc::ty::layout::LayoutOf;