Add none filter

[aaron-hardin]

Resolves issue #724

Still learning Rust, so any feedback would be much appreciated.

[nathanfranke]

#906

diff --git a/src/filters/none.rs b/src/filters/none.rs
index 4616cd8..ba1208e 100644
--- a/src/filters/none.rs
+++ b/src/filters/none.rs
@@ -1,5 +1,5 @@
 //! A filter that matches no route.
-use futures::future;
+use futures_util::future;
 
 use crate::filter::{filter_fn, Filter};
 use crate::reject::{self, Rejection};