Tweak ball shooter mesh to make rviz happy

[caguero]

When launching rviz, its COLLADA parser was complaining about some empty elements. Here's an example:

[ERROR] [1634936987.984769294, 382.378000000]: Could not load resource [package://vrx_gazebo/models/ball_shooter/meshes/ball_shooter_launcher.dae]: Collada: package://vrx_gazebo/models/ball_shooter/meshes/ball_shooter_launcher.dae - Expected end of <keywords> element.

How to test it:

roslaunch vrx_gazebo vrx.launch extra_gazebo_args:="--verbose"

roslaunch wamv_gazebo localization_example.launch

roslaunch wamv_gazebo rviz_vrx.launch

You shouldn't see any errors in the rviz terminal.

[M1chaelM]

I see only errors related to TF_REPEATED_DATA, which are addressed by PR #382. The Collada complaints are gone.