Add redis.sessions.cookie_max_age to dev INI file

I don't think there was any particular reason this wasn't included, and
makes the behavior closer to what it is in production.

tildes/development.ini

@@ -29,6 +29,7 @@ redis.sessions.secret = completely_insecure_secret
 redis.sessions.unix_socket_path = %(redis.unix_socket_path)s
 redis.sessions.prefix = session:
 redis.sessions.cookie_secure = true
+redis.sessions.cookie_max_age = 31536000
 
 # Set session timeout to 10 mins by default, we'll extend it when people log in
 redis.sessions.timeout = 600