Use HTTPS for all Nominatim requests.

HTTP support will be discontinued according to this:
https://lists.openstreetmap.org/pipermail/geocoding/2018-January/001918.html

Fixes #1267

lib/geocoder/lookups/nominatim.rb

@@ -9,7 +9,7 @@ module Geocoder::Lookup
     end
 
     def map_link_url(coordinates)
-      "http://www.openstreetmap.org/?lat=#{coordinates[0]}&lon=#{coordinates[1]}&zoom=15&layers=M"
+      "https://www.openstreetmap.org/?lat=#{coordinates[0]}&lon=#{coordinates[1]}&zoom=15&layers=M"
     end
 
     def query_url(query)
@@ -18,6 +18,10 @@ module Geocoder::Lookup
       "#{protocol}://#{host}/#{method}?" + url_query_string(query)
     end
 
+    def supported_protocols
+      [:https]
+    end
+
     private # ---------------------------------------------------------------
 
     def results(query)