Call clear_active_connections! or clear_all_connections! always!

https://github.com/sonots/activerecord-refresh_connection/pull/1 introduces `max_requests` parameter but it contains a problem; when `clear_all_connections!` is not called, neither `clear_all_connections!` nor `clear_all_connections!` is called.

With this PR, `clear_active_connections!` will be called when `clear_all_connections!` is not called.

Thank you for pointing this out: https://twitter.com/kamipo/status/512179728896122880