Fix build error on latest nightly (#35)

toku-sa-n · web-flow · commit 8f75bed7f4de · 2020-09-24T10:32:22.000+02:00
See: rust-lang/rust#77134
diff --git a/src/lib.rs b/src/lib.rs
@@ -1,4 +1,4 @@
-#![feature(const_fn)]
+#![feature(const_mut_refs)]
 #![cfg_attr(
     feature = "alloc_ref",
     feature(allocator_api, alloc_layout_extra, nonnull_slice_from_raw_parts)

Original file line number	Diff line number	Diff line change
`@@ -1,4 +1,4 @@`
`1`		`-#![feature(const_fn)]`
	`1`	`+#![feature(const_mut_refs)]`
`2`	`2`	`#![cfg_attr(`
`3`	`3`	`feature = "alloc_ref",`
`4`	`4`	`feature(allocator_api, alloc_layout_extra, nonnull_slice_from_raw_parts)`