bump libreoffice version to non-archived version
bump libreoffice version to non-archived version

 * The LibreOffice download archive has been down since Jan. 22,
   2019.  Bump to a maintained version (v6.1.5) that is available from
   the main download site.

felliott/modular-file-renderer,felliott/modular-file-renderer,CenterForOpenScience/modular-file-renderer,felliott/modular-file-renderer,CenterForOpenScience/modular-file-renderer,CenterForOpenScience/modular-file-renderer,CenterForOpenScience/modular-file-renderer,felliott/modular-file-renderer