Update based on changes to redis-rb gem v4.0.

[] and []= methods were removed.

examples/autoexpire_cache_redis.rb

@@ -8,11 +8,11 @@ class AutoexpireCacheRedis
   end
 
   def [](url)
-    @store.[](url)
+    @store.get(url)
   end
 
   def []=(url, value)
-    @store.[]=(url, value)
+    @store.set(url, value)
     @store.expire(url, @ttl)
   end
 
@@ -25,4 +25,4 @@ class AutoexpireCacheRedis
   end
 end
 
-Geocoder.configure(:cache => AutoexpireCacheRedis.new(Redis.new))
\ No newline at end of file
+Geocoder.configure(:cache => AutoexpireCacheRedis.new(Redis.new))