title: can't do http request with async and await
body: <p>Trying to use <code>async</code> and <code>await</code> to do http request in nodejs, but got error. Any ideas? Thx</p>
  
  <pre><code>got response: 
  undefined
  /home/tom/learn/node/node_modules/node-rest-client/lib/node-rest-client.js:539
              callback(parsedData,res);
              ^
  
  TypeError: callback is not a function
      at /home/tom/learn/node/node_modules/node-rest-client/lib/node-rest-client.js:539:13
      at Object.parse (/home/tom/learn/node/node_modules/node-rest-client/lib/nrc-parser-manager.js:151:3)
      at ConnectManager.handleResponse (/home/tom/learn/node/node_modules/node-rest-client/lib/node-rest-client.js:538:32)
      at ConnectManager.handleEnd (/home/tom/learn/node/node_modules/node-rest-client/lib/node-rest-client.js:531:18)
      at IncomingMessage.&lt;anonymous&gt; (/home/tom/learn/node/node_modules/node-rest-client/lib/node-rest-client.js:678:34)
      at emitNone (events.js:110:20)
      at IncomingMessage.emit (events.js:207:7)
      at endReadableNT (_stream_readable.js:1059:12)
      at _combinedTickCallback (internal/process/next_tick.js:138:11)
      at process._tickCallback (internal/process/next_tick.js:180:9)
  </code></pre>
  
  <p>Here is the source code for the script</p>
  
  <pre><code>var Client = require('node-rest-client').Client;
  var client = new Client();
  async function test1() {
      response = await client.get("http://localhost/tmp.txt");
      console.log("got response: ");
      console.log(response.headers);
  };
  test1();
  </code></pre>
  
  <p>nodejs is of version v8.4.0, on ubuntu 14.04. </p>