Remove argument from use_hook closure (#496)

Also; update docs for said function

packages/router/src/hooks/use_router.rs

@@ -3,7 +3,7 @@ use dioxus::core::ScopeState;
 
 /// This hook provides access to the `RouterService` for the app.
 pub fn use_router(cx: &ScopeState) -> &RouterService {
-    cx.use_hook(|_| {
+    cx.use_hook(|| {
         cx.consume_context::<RouterService>()
             .expect("Cannot call use_route outside the scope of a Router component")
     })