get_action! no need to specify the type

we already cast it to a gio::SimpleAction
hence the compiler can figure out the type

src/lib.rs

@@ -57,7 +57,7 @@ macro_rules! get_action {
     }};
 
     ($actions:expr, $name:ident) => {
-        let $name: gio::SimpleAction = $actions
+        let $name = $actions
             .lookup_action(stringify!($name))
             .expect(&format!("Could not find action \"{}\"", stringify!($name)))
             .downcast::<gio::SimpleAction>()