Node v6 fix

index.js

@@ -110,5 +110,5 @@ module.exports = {
   Transport,
   ConnectionPool,
   Serializer,
-  ...symbols
+  symbols
 }

test/unit/client.test.js

@@ -2,7 +2,8 @@
 
 const { test } = require('tap')
 const { URL } = require('url')
-const { Client, kConnectionPool } = require('../../index')
+const { Client, symbols } = require('../../index')
+const { kConnectionPool } = symbols
 
 test('Configure host', t => {
   t.test('Single string', t => {