Fix order of template arguments in Handler documentation example (#3566)

Fix order of template arguments in doc

Author: justahero

actix-web/src/handler.rs

@@ -70,7 +70,7 @@ use crate::{
 /// This is the source code for the 2-parameter implementation of `Handler` to help illustrate the
 /// bounds of the handler call after argument extraction:
 /// ```ignore
-/// impl<Func, Arg1, Arg2, Fut> Handler<(Arg1, Arg2)> for Func
+/// impl<Func, Fut, Arg1, Arg2> Handler<(Arg1, Arg2)> for Func
 /// where
 ///     Func: Fn(Arg1, Arg2) -> Fut + Clone + 'static,
 ///     Fut: Future,