Issue with 6DOF mesh loading

Hello, the XACRO file located at `FLAIR/kortex_description/arms/gen3/6dof/urdf/gen3_macro.xacro` is trying to load 6DOF “.STL” files, but within `FLAIR/kortex_description/arms/gen3/6dof/meshes` the meshes have ".stl" extensions, so `kinova.launch` cannot load part of the robot model. Maybe a simple fix could be just renaming ".stl" -> ".STL"?