When I try to run the heatmap notebook for example I get the error: ``` --------------------------------------------------------------------------- AttributeError Traceback (most recent call last) <ipython-input-5-d6c6ea6c7974> in <module>() 1 corners = [(markers.loc[p].lat, markers.loc[p].lon) for p in 'ABDC'] ----> 2 area_polygon = folium.features.PolygonMarker(corners, fill_opacity=0.) AttributeError: module 'folium.features' has no attribute 'PolygonMarker' ``` Is there something wrong with my version of folium?