collision link6.obj is incorrect

Hello,

Thanks for sharing the panda URDF and meshes.

Just wanted to point out that the link6.obj collision mesh is not correct - 1) this is a visual mesh rather than collision mesh; 2) the orientation is 90 deg off.

It would be great to fix this if anybody has time! I've been using it for a while and just found this issue during debugging.

Thank you!