Fix for R 3.5
Fix for R 3.5

USGS-VIZLAB/vizlab,aappling-usgs/vizlab,ldecicco-USGS/vizlab,USGS-VIZLAB/vizlab,aappling-usgs/vizlab,ldecicco-USGS/vizlab,aappling-usgs/vizlab,USGS-VIZLAB/vizlab,ldecicco-USGS/vizlab