Windows - SSL Error (certificate verify failed) with bundle

**Note** - Under WSL it works, but not under Windows

When i use (this also doesn't work on WSL)
```
requests.get('https://domain', verify='/path/to/my/bundle')
```
I get:
```
>>> requests.get('https://google.de', verify='C:/Users/i01002704/Documents/SSL-Certificate_Chain_PEM/k')
Traceback (most recent call last):
  File "C:\Users\i01002704\AppData\Local\Programs\Python\Python36-32\lib\site-packages\urllib3\contrib\pyopenssl.py", line 441, in wrap_socket
    cnx.do_handshake()
  File "C:\Users\i01002704\AppData\Local\Programs\Python\Python36-32\lib\site-packages\OpenSSL\SSL.py", line 1806, in do_handshake
    self._raise_ssl_error(self._ssl, result)
  File "C:\Users\i01002704\AppData\Local\Programs\Python\Python36-32\lib\site-packages\OpenSSL\SSL.py", line 1546, in _raise_ssl_error
    _raise_current_error()
  File "C:\Users\i01002704\AppData\Local\Programs\Python\Python36-32\lib\site-packages\OpenSSL\_util.py", line 54, in exception_from_error_queue
    raise exception_type(errors)
OpenSSL.SSL.Error: [('SSL routines', 'tls_process_server_certificate', 'certificate verify failed')]

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "C:\Users\i01002704\AppData\Local\Programs\Python\Python36-32\lib\site-packages\urllib3\connectionpool.py", line 595, in urlopen
    self._prepare_proxy(conn)
  File "C:\Users\i01002704\AppData\Local\Programs\Python\Python36-32\lib\site-packages\urllib3\connectionpool.py", line 816, in _prepare_proxy
    conn.connect()
  File "C:\Users\i01002704\AppData\Local\Programs\Python\Python36-32\lib\site-packages\urllib3\connection.py", line 326, in connect
    ssl_context=context)
  File "C:\Users\i01002704\AppData\Local\Programs\Python\Python36-32\lib\site-packages\urllib3\util\ssl_.py", line 329, in ssl_wrap_socket
    return context.wrap_socket(sock, server_hostname=server_hostname)
  File "C:\Users\i01002704\AppData\Local\Programs\Python\Python36-32\lib\site-packages\urllib3\contrib\pyopenssl.py", line 448, in wrap_socket
    raise ssl.SSLError('bad handshake: %r' % e)
ssl.SSLError: ("bad handshake: Error([('SSL routines', 'tls_process_server_certificate', 'certificate verify failed')],)",)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "C:\Users\i01002704\AppData\Local\Programs\Python\Python36-32\lib\site-packages\requests\adapters.py", line 440, in send
    timeout=timeout
  File "C:\Users\i01002704\AppData\Local\Programs\Python\Python36-32\lib\site-packages\urllib3\connectionpool.py", line 639, in urlopen
    _stacktrace=sys.exc_info()[2])
  File "C:\Users\i01002704\AppData\Local\Programs\Python\Python36-32\lib\site-packages\urllib3\util\retry.py", line 388, in increment
    raise MaxRetryError(_pool, url, error or ResponseError(cause))
urllib3.exceptions.MaxRetryError: HTTPSConnectionPool(host='google.de', port=443): Max retries exceeded with url: / (Caused by SSLError(SSLError("bad handshake: Error([('SSL routines', 'tls_process_server_certificate', 'certificate verify failed')],)",),))

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "C:\Users\i01002704\AppData\Local\Programs\Python\Python36-32\lib\site-packages\requests\api.py", line 72, in get
    return request('get', url, params=params, **kwargs)
  File "C:\Users\i01002704\AppData\Local\Programs\Python\Python36-32\lib\site-packages\requests\api.py", line 58, in request
    return session.request(method=method, url=url, **kwargs)
  File "C:\Users\i01002704\AppData\Local\Programs\Python\Python36-32\lib\site-packages\requests\sessions.py", line 508, in request
    resp = self.send(prep, **send_kwargs)
  File "C:\Users\i01002704\AppData\Local\Programs\Python\Python36-32\lib\site-packages\requests\sessions.py", line 618, in send
    r = adapter.send(request, **kwargs)
  File "C:\Users\i01002704\AppData\Local\Programs\Python\Python36-32\lib\site-packages\requests\adapters.py", line 506, in send
    raise SSLError(e, request=request)
requests.exceptions.SSLError: HTTPSConnectionPool(host='google.de', port=443): Max retries exceeded with url: / (Caused by SSLError(SSLError("bad handshake: Error([('SSL routines', 'tls_process_server_certificate', 'certificate verify failed')],)",),))
```

Another try was using path to directory where certificates are stored instead of bundle (this works on WSL)
/path/to/certs/
which looks like:
![image](https://user-images.githubusercontent.com/30751516/40360073-21d5853a-5dc5-11e8-910b-ee83343cd8a5.png)

I created the bundle with:
```
cat File1 File2 File3 >> bundle.pem
```

I always get this error. Why? I hope you can help me.

i can make request without cert bundle. nvm. it works now behind proxy.....