message: use correct feature gate
diff: #![cfg_attr(feature = "no-std", no_std)]
  #![cfg_attr(
  - all(feature = "no-std", not(any(test, doc))),
  + all(feature = "provide-allocator", not(any(test, doc))),
  feature(alloc_error_handler, core_intrinsics, lang_items)
  )]
  #![doc(html_root_url = "https://docs.rs/casper-contract/1.0.0")]
  @@ -64,7 +64,7 @@ extern crate alloc;
  pub mod contract_api;
  pub mod ext_ffi;
  -#[cfg(all(feature = "no-std", not(any(test, doc))))]
  +#[cfg(all(feature = "provide-allocator", not(any(test, doc))))]
  mod no_std_handlers;
  pub mod unwrap_or_revert;
  