Don't list #keys method as required.

README.md

@@ -472,7 +472,6 @@ This example uses Redis, but the cache store can be any object that supports the
 
 * `store#[](key)` or `#get` or `#read` - retrieves a value
 * `store#[]=(key, value)` or `#set` or `#write` - stores a value
-* `store#keys` - lists all keys
 * `store#del(url)` - deletes a value
 
 Even a plain Ruby hash will work, though it's not a great choice (cleared out when app is restarted, not shared between app instances, etc).