This can solve the problem only when previewing the scans.
If you want to further create the map or do the navigation, there is an additional node in tutorial_pkg named drive_controller_node. This node is publishing the tf transform between base_link and odom frames.
You can start this node manually or use one of the launch files in the package.
To test mapping possibility, you can use tutorial_6_core.launch, this contain the rosbot_hardware.launch, gmapping.launch and drive_controller_node.
Also, please update the tutorial_pkg repository, as there are small updates introduced today.
There are appropriate launch files.
The tutorial_7_core.launch allow to set a goal point, plan a path and autonomously drive to it.
The tutorial_8_core.launch allow to autonomously explore all accessible places while building a map.
Their usage is explained in details in tutorials.