Feature Request: add support for scatterpolar

[JeffSolomon]

plotly/plotly.js#2200 fixes a number of issues with polar plots, but adds a new trace type (scatterpolar) that cannot currently be created through plotly.py

[cldougl]

Hi there- you can now upgrade to version 2.3.0 of this library to use those features offline (as with plotly.js)