make folium code examples compatible with latest pyproj version

[stijnvanhoey]

Some of the current tutorial notebooks use a small support function to convert coordinates, making plotting with folium possible. Runnning them currently provides a lot of FutureWarning. As such, make sure to update the code of convert_latlon to make it compatible with newer pyproj versions:

from pyproj import Transformer

# convert the coordinates to lat/lon for folium
def convert_latlon(x1, y1):
    transformer = Transformer.from_crs("epsg:31370", "epsg:4326", always_xy=True)
    x2,y2 = transformer.transform(x1, y1)
    return x2, y2

[stijnvanhoey]

Note: this is more future proof than adding import warnings; warnings.simplefilter('ignore') ;-)