title: Modify styling options for holoviews sankey graph
body: <p>Is it possible to modify Node style in a holoviews (v 1.10.4) Sankey diagram backed by bokeh (v 0.12.16)? I am setting the node_line_color using the options method (also tried via %%opts in Jupiter notebook) however it is ignored and I see a black outline (default) instead of the white I specify. Only the node_width attribute seems to work but all other node styling attributes are ignored.</p>
  
  <pre><code>import pandas as pd
  import holoviews as hv
  
  hv.extension('bokeh')
  edges = pd.read_csv('data.csv')
  hv.Sankey(edges).options(node_line_color='white')
  </code></pre>