[lua] focus type parameter for lua/coroutine

std/lua/Coroutine.hx

@@ -64,7 +64,7 @@ extern class Coroutine<T:Function> extends Thread {
 		The coroutine cannot be running a C function, a metamethod, or an iterator.
 		Any arguments to `yield` are passed as extra results to `resume`.
 	**/
-	public static function yield(args : Rest<Dynamic>) : Dynamic;
+	public static function yield<T>(args : Rest<T>) : T;
 
 	/**
 		Creates a new coroutine, with body `f`.