Speed up Travis check_source jobs
Speed up Travis check_source jobs

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