Adapt to changed leaflet-control-geocoder behaviour

Apparently, the object returned by requiring `leaflet-control-geocoder`
appears to be an empty object, so calling a function on it was failing.
It can be accessed via the `L.Control.Geocoder` object though, so take
that route.

Author: mstock

src/index.js

@@ -92,9 +92,8 @@ function makeIcon(i, n) {
     });
   }
 }
-
 var plan = new ReversablePlan([], {
-  geocoder: Geocoder.nominatim(),
+  geocoder: L.Control.Geocoder.nominatim(),
   routeWhileDragging: true,
   createMarker: function(i, wp, n) {
     var options = {