Update spin.d.ts

`spin()` expects an HTMLElement, `JQuery` type won't work for example.

spin/spin.d.ts

@@ -34,7 +34,7 @@ declare class Spinner {
      * spinning, it is automatically removed from its previous target by calling
      * stop() internally.
      */
-    spin(target?: any): Spinner;
+    spin(target?: HTMLElement): Spinner;
 
     /**
      * Stops and removes the Spinner.