Replace usages of 'bad_style' with 'nonstandard_style'.

`bad_style` is being deprecated in favor of `nonstandard_style`:

- https://github.com/rust-lang/rust/issues/41646

src/libstd/sys/windows/c.rs

@@ -10,7 +10,7 @@
 
 //! C definitions used by libnative that don't belong in liblibc
 
-#![allow(bad_style)]
+#![allow(nonstandard_style)]
 #![cfg_attr(test, allow(dead_code))]
 #![unstable(issue = "0", feature = "windows_c")]
 

src/libstd/sys/windows/mod.rs

@@ -8,7 +8,7 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#![allow(missing_docs, bad_style)]
+#![allow(missing_docs, nonstandard_style)]
 
 use ptr;
 use ffi::{OsStr, OsString};

src/libstd/sys/windows/os.rs

@@ -10,7 +10,7 @@
 
 //! Implementation of `std::os` functionality for Windows
 
-#![allow(bad_style)]
+#![allow(nonstandard_style)]
 
 use os::windows::prelude::*;