Fix row_header attribute input to DataTable (#1872)
Fix row_header attribute input to DataTable (#1872)

This was changed in 0.12.15

See https://github.com/bokeh/bokeh/issues/7719 for details
dask/distributed,mrocklin/distributed,mrocklin/distributed,dask/distributed,mrocklin/distributed,blaze/distributed,dask/distributed,blaze/distributed,dask/distributed