Make get_nndc_data.py compatible with Python 3.
Make get_nndc_data.py compatible with Python 3.

paulromano/openmc,lilulu/openmc,samuelshaner/openmc,smharper/openmc,mit-crpg/openmc,mjlong/openmc,amandalund/openmc,shikhar413/openmc,wbinventor/openmc,smharper/openmc,samuelshaner/openmc,paulromano/openmc,mit-crpg/openmc,bhermanmit/openmc,lilulu/openmc,nhorelik/openmc,liangjg/openmc,sxds/opemmc,bhermanmit/openmc,shenqicang/openmc,shikhar413/openmc,samuelshaner/openmc,walshjon/openmc,mit-crpg/openmc,smharper/openmc,walshjon/openmc,samuelshaner/openmc,wbinventor/openmc,amandalund/openmc,paulromano/openmc,shenqicang/openmc,liangjg/openmc,smharper/openmc,johnnyliu27/openmc,shikhar413/openmc,lilulu/openmc,shikhar413/openmc,kellyrowland/openmc,sxds/opemmc,johnnyliu27/openmc,liangjg/openmc,wbinventor/openmc,wbinventor/openmc,mit-crpg/openmc,kellyrowland/openmc,johnnyliu27/openmc,amandalund/openmc,nhorelik/openmc,walshjon/openmc,mjlong/openmc,paulromano/openmc,amandalund/openmc,liangjg/openmc,johnnyliu27/openmc,walshjon/openmc