title: Unexpected Error while executing imgkit
body: <p>I'm a newbie to Python, While learning imgkit (PI module) I got this error which was not expected for a simple code. Below is the code </p>
  
  <pre><code>import imgkit
  
  imgkit.from_url('https://www.google.co.in/','fs.jpg')
  </code></pre>
  
  <p>and the error which I got is </p>
  
  <pre><code>Traceback (most recent call last):
    File "G:\python\lib\site-packages\imgkit-0.1.8-py3.6.egg\imgkit\config.py", line 30, in __init__
      with open(self.wkhtmltoimage):
  FileNotFoundError: [Errno 2] No such file or directory: b''
  
  During handling of the above exception, another exception occurred:
  
  Traceback (most recent call last):
    File "C:\Users\ALEXANDER\Desktop\def img.py", line 3, in &lt;module&gt;
      imgkit.from_url('https://www.google.co.in/','fs.jpg')
    File "G:\python\lib\site-packages\imgkit-0.1.8-py3.6.egg\imgkit\api.py", line 20, in from_url
      rtn = IMGKit(url, 'url', options=options, toc=toc, cover=cover, config=config, cover_first=cover_first)
    File "G:\python\lib\site-packages\imgkit-0.1.8-py3.6.egg\imgkit\imgkit.py", line 34, in __init__
      self.config = Config() if not config else config
    File "G:\python\lib\site-packages\imgkit-0.1.8-py3.6.egg\imgkit\config.py", line 36, in __init__
      'http://wkhtmltopdf.org\n'.format(self.wkhtmltoimage))
  OSError: No wkhtmltoimage executable found: "b''"
  If this file exists please check that this process can read it. Otherwise please install wkhtmltopdf - http://wkhtmltopdf.org
  </code></pre>
  
  <p>Could anyone tell me what mistake I have done.</p>