SyntaxError: Syntax error: Expected "none" or at least one resinfo

[niftylettuce]

Yet another bug with this package, can you help Scott?

```sh
Traceback (most recent call last):
 File "/var/www/production/source/node_modules/dkimpy/scripts/arcsign.py", line 79, in <module>
   main()
 File "/var/www/production/source/node_modules/dkimpy/scripts/arcsign.py", line 70, in main
   srv_id, cv, linesep=dkim.util.get_linesep(message))
 File "/home/deploy/.local/lib/python3.6/site-packages/dkim/__init__.py", line 1399, in arc_sign
   timestamp=timestamp, standardize=standardize)
 File "/home/deploy/.local/lib/python3.6/site-packages/dkim/__init__.py", line 1025, in sign
   for res in ar_headers]
 File "/home/deploy/.local/lib/python3.6/site-packages/dkim/__init__.py", line 1025, in <listcomp>
   for res in ar_headers]
 File "/home/deploy/.local/lib/python3.6/site-packages/authres/__init__.py", line 206, in parse
   return authres.core.AuthenticationResultsHeader.parse(core_features(), string)
 File "/home/deploy/.local/lib/python3.6/site-packages/authres/core.py", line 442, in parse
   return self.parse_value(feature_context, string)
 File "/home/deploy/.local/lib/python3.6/site-packages/authres/core.py", line 454, in parse_value
   header._parse()
 File "/home/deploy/.local/lib/python3.6/site-packages/authres/core.py", line 523, in _parse
   raise SyntaxError('Expected "none" or at least one resinfo', self._parse_text)
authres.core.SyntaxError: Syntax error: Expected "none" or at least one resinfo at: smtp.user=<hidden>; auth=pass (LOGIN)
```

[Scott Kitterman (kitterman)]

This looks like the calling application isn't providing all the needed information, not a bug in dkimpy. If you feel differently, please feel free to reopen with details on how to replicate the problem.