Fix DeprecationWarning in _get_summary
Fix DeprecationWarning in _get_summary

logging.warn is deprecated, should be replaced with .warning.

ehashman/pelican,karlcow/pelican,douglaskastle/pelican,Scheirle/pelican,Rogdham/pelican,lucasplus/pelican,zackw/pelican,ingwinlu/pelican,catdog2/pelican,catdog2/pelican,zackw/pelican,GiovanniMoretti/pelican,ehashman/pelican,ehashman/pelican,iKevinY/pelican,douglaskastle/pelican,farseerfc/pelican,zackw/pelican,iKevinY/pelican,lucasplus/pelican,getpelican/pelican,douglaskastle/pelican,karlcow/pelican,talha131/pelican,Scheirle/pelican,karlcow/pelican,Rogdham/pelican,avaris/pelican,Rogdham/pelican,lucasplus/pelican,farseerfc/pelican,catdog2/pelican,GiovanniMoretti/pelican,talha131/pelican,avaris/pelican,Scheirle/pelican,GiovanniMoretti/pelican,getpelican/pelican,ingwinlu/pelican