Add LD_LIBRARY_PATH to finish-args
    
    This used to come hardcoded from flatpak-module-tools, but was removed
    in flatpak-module-tools 0.11.2. This commit moves it here so that we
    don't lose LD_LIBRARY_PATH.
    
    See https://bodhi.fedoraproject.org/updates/FEDORA-FLATPAK-2020-30fe5a648b