fix comment

src/ngx_http_push_stream_module_subscriber.c

@@ -158,7 +158,7 @@ ngx_http_push_stream_subscriber_handler(ngx_http_request_t *r)
     ngx_http_push_stream_disconnect_timer_set(cf);
     ngx_http_push_stream_ping_timer_set(cf);
 
-    // turn on timer to cleanup memory of old messages an channels
+    // turn on timer to cleanup memory of old messages and channels
     ngx_http_push_stream_memory_cleanup_timer_set(cf);
 
     ngx_destroy_pool(temp_pool);