fix alloc warnings?

Author: yoshuawuyts

src/collections/vec.rs

@@ -8,6 +8,7 @@
 use crate::concurrent_stream::{self, ConcurrentStream, FromStream};
 use crate::prelude::*;
 use crate::utils::{from_iter, FromIter};
+#[cfg(all(feature = "alloc", not(feature = "std")))]
 use alloc::vec::Vec;
 use core::future::Ready;
 

src/concurrent_stream/for_each.rs

@@ -1,8 +1,8 @@
+use super::{Consumer, ConsumerState};
 use crate::future::FutureGroup;
 use futures_lite::StreamExt;
 use pin_project::pin_project;
 
-use super::{Consumer, ConsumerState};
 use alloc::sync::Arc;
 use core::future::Future;
 use core::marker::PhantomData;

src/concurrent_stream/from_concurrent_stream.rs

@@ -1,5 +1,6 @@
 use super::{ConcurrentStream, Consumer, ConsumerState, IntoConcurrentStream};
 use crate::future::FutureGroup;
+#[cfg(all(feature = "alloc", not(feature = "std")))]
 use alloc::vec::Vec;
 use core::future::Future;
 use core::pin::Pin;