Unauthorized Crawlera Header: "x-crawlera-session" Error

Trying to run the example with my API key returns the following response:

```html
<html><head></head>
    <body><pre style="word-wrap: break-word; white-space: pre-wrap;">
       Unauthorized Crawlera Header: "x-crawlera-session"
    </pre>
  </body>
</html>
```