hvplots doesn't work with plotly extension

[nstrayer]

As of #4335, basic hvplot plots work, but if you switch to plotly as the rendering extension things still don't work.

import hvplot.pandas
from bokeh.sampledata.penguins import data as df

hvplot.extension('plotly')

df.hvplot.scatter(x='bill_length_mm', y='bill_depth_mm', by='species')