[fix] Restore compatibility with Node.js < 6.13.0

Fixes #1472

Author: lpinca

lib/websocket.js

@@ -6,7 +6,7 @@ const https = require('https');
 const http = require('http');
 const net = require('net');
 const tls = require('tls');
-const { URL } = require('url');
+const url = require('url');
 
 const PerMessageDeflate = require('./permessage-deflate');
 const EventTarget = require('./event-target');
@@ -464,7 +464,10 @@ function initAsClient(address, protocols, options) {
     parsedUrl = address;
     this.url = address.href;
   } else {
-    parsedUrl = new URL(address);
+    //
+    // The WHATWG URL constructor is not available on Node.js < 6.13.0
+    //
+    parsedUrl = url.URL ? new url.URL(address) : url.parse(address);
     this.url = address;
   }