version bump --> 1.6.15 (widget save + to_dataframe)
version bump --> 1.6.15 (widget save + to_dataframe)

plotly/python-api,plotly/python-api,plotly/plotly.py,plotly/python-api,ee-in/python-api,ee-in/python-api,ee-in/python-api,plotly/plotly.py,plotly/plotly.py