Fix test_image_overlay for py27
Fix test_image_overlay for py27

shankari/folium,QuLogic/folium,ocefpaf/folium,python-visualization/folium,talespaiva/folium,shankari/folium,QuLogic/folium,shankari/folium,talespaiva/folium,ocefpaf/folium,talespaiva/folium,talespaiva/folium,python-visualization/folium,QuLogic/folium