Fix(no_std): boxed not in collections

Author: kamarkiewicz

src/lib.rs

@@ -385,13 +385,16 @@
 //! ```
 #![cfg_attr(not(feature = "std"), feature(no_std))]
 #![cfg_attr(not(feature = "std"), feature(collections))]
+#![cfg_attr(not(feature = "std"), feature(alloc))]
 #![cfg_attr(not(feature = "std"), no_std)]
 #![cfg_attr(feature = "nightly", feature(test))]
 #![cfg_attr(feature = "nightly", feature(const_fn))]
 #![cfg_attr(feature = "nightly", feature(plugin))]
 #![cfg_attr(feature = "nightly", plugin(compiler_error))]
 //#![warn(missing_docs)]
 
+#[cfg(not(feature = "std"))]
+extern crate alloc;
 #[cfg(not(feature = "std"))]
 extern crate collections;
 #[cfg(feature = "regexp")]
@@ -415,7 +418,8 @@ macro_rules! compiler_error {
 mod std {
 #[macro_use]
   pub use core::{fmt, cmp, iter, option, result, ops, slice, str, mem, convert};
-  pub use collections::{boxed, vec, string};
+  pub use alloc::boxed;
+  pub use collections::{vec, string};
   pub mod prelude {
     pub use core::prelude as v1;
   }