Added support for specular shininess parameter

Added support for exporting of the shininess parameter (hardness of the specular color of a material). It was not exported from an input model before.

Just one line of code changed + added some white space.

Proposed modification can be easily tested by comparing conversion of samples/cube.dae model to .g3dj before and after applying the pull request (fbx-conv cube.dae cube.g3dj)

Regards,
Jarek