Add missing getDefCommand for Sponge - Fixes #75

sponge/src/main/java/co/aikar/commands/SpongeRootCommand.java

@@ -111,6 +111,11 @@ public class SpongeRootCommand implements CommandCallable, RootCommand {
         addChildShared(this.children, this.subCommands, command);
     }
 
+    @Override
+    public BaseCommand getDefCommand(){
+        return defCommand;
+    }
+
     @Override
     public CommandManager getManager() {
         return manager;