Show that we do not support nominatim 4.x (#200)

Author: Nyholm

composer.json

@@ -53,7 +53,8 @@
     "geocoder-php/mapquest-provider": "^4.0"
   },
   "conflict":  {
-    "willdurand/geocoder": "3.2"
+    "willdurand/geocoder": "3.2",
+    "geocoder-php/nominatim-provider": "<5.0"
   },
   "autoload": {
     "psr-4": {