Fix warning on latest nightly

Amanieu · Amanieu · commit 373a9d4203a9 · 2019-04-16T01:55:11.000+01:00
diff --git a/src/lib.rs b/src/lib.rs
@@ -13,7 +13,6 @@
 #![cfg_attr(
     feature = "nightly",
     feature(
-        alloc,
         alloc_layout_extra,
         allocator_api,
         ptr_offset_from,
