add python3.6 to supported versions in setup.py
add python3.6 to supported versions in setup.py

markelg/xray,shoyer/xarray,pydata/xarray,xray/xray,markelg/xray,rabernat/xray,jhamman/xarray,chunweiyuan/xarray,markelg/xray,shoyer/xray,jcmgray/xarray,jhamman/xray,pydata/xarray,jhamman/xarray,rabernat/xray,pydata/xarray,shoyer/xarray,jhamman/xarray