title: Curl is configured to use SSL, but we have not been able to determine which SSL backend it is using
body: <p>When I perform <code>pip install thumbor</code> I get the following error:</p>
  
  <pre><code>Traceback (most recent call last):
    File "&lt;string&gt;", line 1, in &lt;module&gt;
    File "/private/var/folders/t9/***********************/T/pip-install-knrabyuy/pycurl/setup.py", line 913, in &lt;module&gt;
      ext = get_extension(sys.argv, split_extension_source=split_extension_source)
    File "/private/var/folders/t9/***********************/T/pip-install-knrabyuy/pycurl/setup.py", line 582, in get_extension
      ext_config = ExtensionConfiguration(argv)
    File "/private/var/folders/t9/***********************/T/pip-install-knrabyuy/pycurl/setup.py", line 99, in __init__
      self.configure()
    File "/private/var/folders/t9/***********************/T/pip-install-knrabyuy/pycurl/setup.py", line 316, in configure_unix
      specify the SSL backend manually.''')
  __main__.ConfigurationError: Curl is configured to use SSL, but we have not been able to determine which SSL backend it is using. Please see PycURL documentation for how to specify the SSL backend manually.
  </code></pre>
  
  <p>I've tried <code>brew install curl</code> (which was successfull) however I get the same error when I perform <code>pip install thumbor</code>.</p>
  
  <p>Any idea why?</p>