stabilise feature(never_type)

Replace feature(never_type) with feature(exhaustive_patterns).
feature(exhaustive_patterns) only covers the pattern-exhaustives checks
that used to be covered by feature(never_type)

src/librustc_lint/lib.rs

@@ -32,6 +32,7 @@
 #![feature(quote)]
 #![feature(rustc_diagnostic_macros)]
 #![feature(slice_patterns)]
+#![cfg_attr(stage0, feature(never_type))]
 
 #[macro_use]
 extern crate syntax;