Add layer definition for Thunderforest's Transport Dark layer

Author: tomhughes

leaflet-osm.js

@@ -44,6 +44,14 @@ L.OSM.TransportMap = L.OSM.TileLayer.extend({
   }
 });
 
+L.OSM.TransportDarkMap = L.OSM.TileLayer.extend({
+  options: {
+    url: 'https://{s}.tile.thunderforest.com/transport-dark/{z}/{x}/{y}{r}.png?apikey={apikey}',
+    maxZoom: 21,
+    attribution: '© <a href="https://www.openstreetmap.org/copyright" target="_blank">OpenStreetMap</a> contributors. Tiles courtesy of <a href="http://www.thunderforest.com/" target="_blank">Andy Allan</a>'
+  }
+});
+
 L.OSM.OPNVKarte = L.OSM.TileLayer.extend({
   options: {
     url: 'https://tileserver.memomaps.de/tilegen/{z}/{x}/{y}.png',