Use consistent feature naming

Author: ecstatic-morse

src/libcore/lib.rs

@@ -72,10 +72,10 @@
 #![feature(concat_idents)]
 #![feature(const_alloc_layout)]
 #![feature(const_if_match)]
-#![feature(const_int_checked)]
-#![feature(const_int_euclidean)]
-#![feature(const_int_overflowing)]
-#![feature(const_int_saturating)]
+#![feature(const_checked_int_methods)]
+#![feature(const_euclidean_int_methods)]
+#![feature(const_overflowing_int_methods)]
+#![feature(const_saturating_int_methods)]
 #![feature(const_int_unchecked_arith)]
 #![feature(const_panic)]
 #![feature(const_fn_union)]