Check if cache store uses read/write for functions.

In addition to checking for []/[]= and set/get, also check
for functions like read/write.

lib/geocoder/cache.rb

@@ -15,6 +15,8 @@ module Geocoder
           store[key_for(url)]
         when store.respond_to?(:get)
           store.get key_for(url)
+        when store.respond_to?(:read)
+          store.read key_for(url)
       end
     end
 
@@ -27,6 +29,8 @@ module Geocoder
           store[key_for(url)] = value
         when store.respond_to?(:set)
           store.set key_for(url), value
+        when store.respond_to?(:write)
+          store.write key_for(url), value
       end
     end