Use our own fork of Leaflet.toolbar, given it's not more maintained

And there is not npm stable release. Let's not depend on a third party
git trunk.

package.json

@@ -50,7 +50,7 @@
     "leaflet-loading": "^0.1.23",
     "leaflet-measurable": "^0.0.2",
     "leaflet-minimap": "^3.4.0",
-    "leaflet-toolbar": "Leaflet/Leaflet.toolbar",
+    "leaflet-toolbar": "umap-project/Leaflet.toolbar",
     "leaflet.heat": "^0.2.0",
     "leaflet.markercluster": "^1.0.0",
     "leaflet.path.drag": "0.0.5",