fix poll notifications test

``` lein test :only pg.client-test/test-client-test-poll-updates FAIL in (test-client-test-poll-updates) (client_test.clj:964) PORT 10120 expected: (= #{{:channel "test", :msg :NotificationResponse, :self? false, :message "1"} {:channel "test", :msg :NotificationResponse, :self? false, :message "2"} {:channel "test", :msg :NotificationResponse, :self? false, :message "3"}} (->> capture! deref (map (fn [fields] (dissoc fields :pid))) (set))) actual: (not (= #{{:channel "test", :msg :NotificationResponse, :self? false, :message "1"} {:channel "test", :msg :NotificationResponse, :self? false, :message "2"} {:channel "test", :msg :NotificationResponse, :self? false, :message "3"}} #{{:channel "test", :msg :NotificationResponse, :self? false, :message "1"} {:channel "test", :msg :NotificationResponse, :self? false, :message "2"}})) lein test pg.concurrency-test ```