Fix mapbox gray

Author: yellow-sky

data_sources/mapbox_gray/metadata.ini

@@ -16,5 +16,5 @@ copyright_link =
 terms_of_use = 
 
 [tms]
-url = http://a.tiles.mapbox.com/v3/examples.map-20v6611k/{z}/{x}/{y}.png
+url = http://api.tiles.mapbox.com/v4/mapbox.light/{z}/{x}/{y}.png?access_token=pk.eyJ1IjoibWFwYm94IiwiYSI6IlhHVkZmaW8ifQ.hAMX5hSW-QnTeRCMAy9A8Q
 zmax = 19