actix-rt: minimize futures dependencies to futures-{channel,util} with default features off (#104)

* build(deps): minimize `futures` deps by using `futures-channel` and `futures-util` directly

* style(actix-rt): enforce spaces around equals in `Cargo.toml`

actix-rt/src/lib.rs

@@ -25,7 +25,7 @@ pub use actix_threadpool as blocking;
 /// This function panics if actix system is not running.
 pub fn spawn<F>(f: F)
 where
-    F: futures::Future<Output = ()> + 'static,
+    F: futures_util::future::Future<Output = ()> + 'static,
 {
     if !System::is_set() {
         panic!("System is not running");