Update the asset manager for only 16ms, not until the next asset is loaded.

https://github.com/libgdx/libgdx/wiki/Managing-your-assets#optimize-loading

spine-libgdx/spine-libgdx-tests/src/com/esotericsoftware/spine/SkeletonAssetManagerTest.java

@@ -75,7 +75,7 @@ public class SkeletonAssetManagerTest extends ApplicationAdapter {
 
 		if (skeleton == null) {
 			// Not loaded yet.
-			assetManager.update();
+			assetManager.update(16);
 			// System.out.println(assetManager.getDiagnostics());
 			if (!assetManager.isFinished()) return;