Update for latest libgdx.

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

@@ -303,7 +303,7 @@ public class NormalMapTest extends ApplicationAdapter {
 
 			TextButton resetButton = new TextButton("Reset", skin);
 			resetButton.getColor().a = 0.66f;
-			window.getButtonTable().add(resetButton).height(20);
+			window.getTitleTable().add(resetButton).height(20);
 
 			window.add(root).expand().fill();
 			window.pack();

spine-libgdx/spine-skeletonviewer/src/com/esotericsoftware/spine/SkeletonViewer.java

@@ -307,7 +307,7 @@ public class SkeletonViewer extends ApplicationAdapter {
 
 			minimizeButton.padTop(-2).padLeft(5);
 			minimizeButton.getColor().a = 0.66f;
-			window.getButtonTable().add(minimizeButton).size(20, 20);
+			window.getTitleTable().add(minimizeButton).size(20, 20);
 
 			ScrollPane skinScroll = new ScrollPane(skinList, skin);
 			skinScroll.setFadeScrollBars(false);