Fix use of fill_type in universe module
Fix use of fill_type in universe module

paulromano/openmc,liangjg/openmc,smharper/openmc,johnnyliu27/openmc,liangjg/openmc,mit-crpg/openmc,johnnyliu27/openmc,mit-crpg/openmc,liangjg/openmc,samuelshaner/openmc,smharper/openmc,walshjon/openmc,mit-crpg/openmc,samuelshaner/openmc,wbinventor/openmc,amandalund/openmc,johnnyliu27/openmc,walshjon/openmc,amandalund/openmc,shikhar413/openmc,walshjon/openmc,smharper/openmc,amandalund/openmc,wbinventor/openmc,samuelshaner/openmc,shikhar413/openmc,walshjon/openmc,paulromano/openmc,bhermanmit/openmc,samuelshaner/openmc,wbinventor/openmc,shikhar413/openmc,shikhar413/openmc,johnnyliu27/openmc,paulromano/openmc,paulromano/openmc,mit-crpg/openmc,amandalund/openmc,bhermanmit/openmc,liangjg/openmc,wbinventor/openmc,smharper/openmc