Remove #![feature(slice_rotate)], as it is stable since Rust 1.26.

README.md

@@ -80,7 +80,7 @@ on the `alloc` crate. This only works on nightly rustc.
 
 The `map` feature, disabled by default, enables the `ManagedMap` enum.
 Its interface is not stable yet and is subject to change.
-It also requires the use of a nightly compiler.
+It also requires the use of a nightly compiler, 1.27 or later.
 
 Usage
 -----

src/lib.rs

@@ -1,6 +1,5 @@
 #![no_std]
 #![cfg_attr(all(feature = "alloc", not(feature = "std")), feature(alloc))]
-#![cfg_attr(feature = "map", feature(slice_rotate))]
 #![cfg_attr(feature = "map", feature(collections_range))]
 
 //! A library that provides a way to logically own objects, whether or not