Smaller font size since last Leaflet update

[alexsegura]

The markers/popups are now smaller.

This seems to be due to changes in Leaflet 1.8

Allow fonts to respect users' browser settings by making the font-size relative to the map container. (You can change the font size on leaflet-container to adjust it if needed.) (https://github.com/Leaflet/Leaflet/pull/7800 by @Chandu-4444)

[alexsegura]

We are using BeautifyMarker, but maybe we would need to use another, more up-to-date custom marker library?

Anyway, the changes need to be done here:

https://github.com/coopcycle/coopcycle-web/blob/28be69c966988d4aa24d0cfa0889d7a260e0e259/js/app/MapHelper.js#L45-L53