Fix alloc feature on stable

Author: vks

src/lib.rs

@@ -53,7 +53,7 @@
 #![cfg_attr(all(feature="alloc", not(feature="std")), feature(alloc))]
 #![cfg_attr(all(feature="simd_support", feature="nightly"), feature(stdsimd))]
 
-#[cfg(all(feature="alloc"))]
+#[cfg(all(feature="alloc", not(feature="std")))]
 extern crate alloc;
 
 #[cfg(feature = "getrandom")]

src/seq/index.rs

@@ -326,7 +326,8 @@ where R: Rng + ?Sized, IndexVec: From<Vec<X>> {
 
 #[cfg(test)]
 mod test {
-    use alloc::vec;
+    #[cfg(feature="std")] use std::vec;
+    #[cfg(all(feature="alloc", not(feature="std")))] use crate::alloc::vec;
     use super::*;
 
     #[test]