require update for new interface for writng compressed XML files
the next release of python-ligo-lw will introduce a new interface for turning on compression when writing XML files. the existing "gz" keyword argument of the write_filename() and write_fileobj() functions, which can be set to True or False, will be replaced with a "compress" keyword argument which can be set to "gz" or None, respectively. the existing "gz" keyword argument will be preserved for compatibility but only for one release cycle. this issue is a reminder to update gstlal after the upcoming python-ligo-lw release, and before the next one.