Set INSTALL_BUNDLE_FILES to ON for Mac builds.
Set INSTALL_BUNDLE_FILES to ON for Mac builds.

Fixes https://github.com/OpenChemistry/avogadrolibs/issues/308

Signed-off-by: Geoff Hutchison <9cf35bacc9f8512ca007341c9e919cf5dc03e0c7@gmail.com>

OpenChemistry/avogadroapp,OpenChemistry/avogadroapp,ghutchis/avogadroapp,ghutchis/avogadroapp,OpenChemistry/avogadroapp,ghutchis/avogadroapp,OpenChemistry/avogadroapp,ghutchis/avogadroapp