unpin package versions for doc build (#1101)
unpin package versions for doc build (#1101)

* unpin package versions for doc build

* typo

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