def expand_key(key)
        digest_key = DigestUtils.pack_urlsafe_base64digest(DigestUtils.digest(key))
        namespace = digest_key[0, 2]
        "sprockets/v#{VERSION}/#{namespace}/#{digest_key}"
      end
def expand_key(key)
        digest_key = DigestUtils.pack_urlsafe_base64digest(DigestUtils.digest(key))
        namespace = digest_key[0, 2]
        "sprockets/v#{VERSION}/#{namespace}/#{digest_key}"
      end
Internal: Expand object cache key into a short String key.

 The String should be under 250 characters so its compatible with
 Memcache.

 key - JSON serializable key

 Returns a String with a length less than 250 characters.