undo command def

app/src/main/java/chess/io/commands/UndoCommand.java

@@ -0,0 +1,16 @@
+package chess.io.commands;
+
+import chess.io.Command;
+import chess.io.CommandResult;
+import chess.io.OutputSystem;
+import chess.model.Game;
+
+public class UndoCommand extends Command{
+
+	@Override
+	public CommandResult execute(Game game, OutputSystem outputSystem) {
+		//TODO
+		return CommandResult.Moved;
+	}
+	
+}