Keep the fields of RangeInclusive unstable.

src/liballoc/lib.rs

@@ -123,6 +123,7 @@
 #![feature(on_unimplemented)]
 #![feature(exact_chunks)]
 #![feature(pointer_methods)]
+#![feature(inclusive_range_fields)]
 
 #![cfg_attr(not(test), feature(fn_traits, placement_new_protocol, swap_with_slice, i128))]
 #![cfg_attr(test, feature(test, box_heap))]