nginx import -> Name or service not known

Here are logs at import time, behind a proxy:
```
Importing data from nginx
Traceback (most recent call last):
File "/usr/local/lib/python3.8/site-packages/urllib3/connection.py", line 169, in _new_conn
conn = connection.create_connection(
File "/usr/local/lib/python3.8/site-packages/urllib3/util/connection.py", line 73, in create_connection
for res in socket.getaddrinfo(host, port, family, socket.SOCK_STREAM):
File "/usr/local/lib/python3.8/socket.py", line 918, in getaddrinfo
for res in _socket.getaddrinfo(host, port, family, type, proto, flags):
socket.gaierror: [Errno -2] Name or service not known

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/usr/local/lib/python3.8/site-packages/urllib3/connectionpool.py", line 699, in urlopen
httplib_response = self._make_request(
File "/usr/local/lib/python3.8/site-packages/urllib3/connectionpool.py", line 394, in _make_request
conn.request(method, url, **httplib_request_kw)
File "/usr/local/lib/python3.8/site-packages/urllib3/connection.py", line 234, in request
super(HTTPConnection, self).request(method, url, body=body, headers=headers)
File "/usr/local/lib/python3.8/http/client.py", line 1256, in request
self._send_request(method, url, body, headers, encode_chunked)
File "/usr/local/lib/python3.8/http/client.py", line 1302, in _send_request
self.endheaders(body, encode_chunked=encode_chunked)
File "/usr/local/lib/python3.8/http/client.py", line 1251, in endheaders
self._send_output(message_body, encode_chunked=encode_chunked)
File "/usr/local/lib/python3.8/http/client.py", line 1011, in _send_output
self.send(msg)
File "/usr/local/lib/python3.8/http/client.py", line 951, in send
self.connect()
File "/usr/local/lib/python3.8/site-packages/urllib3/connection.py", line 200, in connect
conn = self._new_conn()
File "/usr/local/lib/python3.8/site-packages/urllib3/connection.py", line 181, in _new_conn
raise NewConnectionError(
urllib3.exceptions.NewConnectionError: : Failed to establish a new connection: [Errno -2] Name or service not known

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/usr/local/lib/python3.8/site-packages/requests/adapters.py", line 439, in send
resp = conn.urlopen(
File "/usr/local/lib/python3.8/site-packages/urllib3/connectionpool.py", line 755, in urlopen
retries = retries.increment(
File "/usr/local/lib/python3.8/site-packages/urllib3/util/retry.py", line 574, in increment
raise MaxRetryError(_pool, url, error or ResponseError(cause))
urllib3.exceptions.MaxRetryError: HTTPConnectionPool(host='nginx.org', port=80): Max retries exceeded with url: /en/security_advisories.html (Caused by NewConnectionError(': Failed to establish a new connection: [Errno -2] Name or service not known'))

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "/opt/vulnerablecode/vulnerabilities/management/commands/import.py", line 110, in _import_data
ImportRunner(importer, batch_size).run(cutoff_date=cutoff_date)
File "/opt/vulnerablecode/vulnerabilities/import_runner.py", line 89, in run
process_advisories(data_source)
File "/usr/local/lib/python3.8/contextlib.py", line 75, in inner
return func(*args, **kwds)
File "/opt/vulnerablecode/vulnerabilities/import_runner.py", line 116, in process_advisories
advisory_batches = chain(data_source.updated_advisories(), data_source.added_advisories())
File "/opt/vulnerablecode/vulnerabilities/importers/nginx.py", line 69, in updated_advisories
data = requests.get(self.url).content
File "/usr/local/lib/python3.8/site-packages/requests/api.py", line 75, in get
return request('get', url, params=params, **kwargs)
File "/usr/local/lib/python3.8/site-packages/requests/api.py", line 61, in request
return session.request(method=method, url=url, **kwargs)
File "/usr/local/lib/python3.8/site-packages/requests/sessions.py", line 542, in request
resp = self.send(prep, **send_kwargs)
File "/usr/local/lib/python3.8/site-packages/requests/sessions.py", line 655, in send
r = adapter.send(request, **kwargs)
File "/usr/local/lib/python3.8/site-packages/requests/adapters.py", line 516, in send
raise ConnectionError(e, request=request)
requests.exceptions.ConnectionError: HTTPConnectionPool(host='nginx.org', port=80): Max retries exceeded with url: /en/security_advisories.html (Caused by NewConnectionError(': Failed to establish a new connection: [Errno -2] Name or service not known'))
Failure to import data from nginx. Continuing...
```