perf(config): emqx_bridge default hash pool

apps/emqx_bridge/etc/emqx_bridge.conf

@@ -51,7 +51,7 @@
 #    connect_timeout: "30s"
 #    max_retries: 3
 #    retry_interval = "10s"
-#    pool_type = "random"
+#    pool_type = "hash"
 #    pool_size = 4
 #    enable_pipelining = true
 #    ssl {