Add Python 3.7 to the PyPI trove classifiers in setup.py
Add Python 3.7 to the PyPI trove classifiers in setup.py

These must have been some glitch in the last release to PyPI because these trove classifiers should appear in the leftmost column in https://pypi.org/project/folium/ instead at the very bottom of the README.md txt.
ocefpaf/folium,python-visualization/folium,ocefpaf/folium,python-visualization/folium