The dialog box said to send the error details to the author, so... (running this with Java SE 9.0.1)

com.badlogic.gdx.utils.GdxRuntimeException: java.lang.NoSuchFieldError: overrideIsOver
at com.badlogic.gdx.backends.lwjgl.LwjglApplication$1.run(LwjglApplication.java:130)
Caused by: java.lang.NoSuchFieldError: overrideIsOver
at Roguelike.UI.ButtonKeyboardHelper.add(ButtonKeyboardHelper.java:59)
at Roguelike.UI.ButtonKeyboardHelper.add(ButtonKeyboardHelper.java:39)
at Roguelike.Screens.MainMenuScreen.create(MainMenuScreen.java:136)
at Roguelike.Screens.MainMenuScreen.show(MainMenuScreen.java:161)
at com.badlogic.gdx.Game.setScreen(Game.java:61)
at Roguelike.RoguelikeGame.switchScreen(RoguelikeGame.java:74)
at Roguelike.RoguelikeGame.create(RoguelikeGame.java:69)
at com.badlogic.gdx.backends.lwjgl.LwjglApplication.mainLoop(LwjglApplication.java:146)
at com.badlogic.gdx.backends.lwjgl.LwjglApplication$1.run(LwjglApplication.java:123)