Exporting key raises ValueError

[a9rkzz]

Upon attempting to export a key, the following exception is raised

Exception in thread Thread-4:
Traceback (most recent call last):
  File "/usr/local/Cellar/python3/3.6.3/Frameworks/Python.framework/Versions/3.6/lib/python3.6/threading.py", line 916, in _bootstrap_inner
    self.run()
  File "/usr/local/Cellar/python3/3.6.3/Frameworks/Python.framework/Versions/3.6/lib/python3.6/threading.py", line 864, in run
    self._target(*self._args, **self._kwargs)
  File "/usr/local/lib/python3.6/site-packages/gnupg/_meta.py", line 650, in _read_response
    result._handle_status(keyword, value)
  File "/usr/local/lib/python3.6/site-packages/gnupg/_parsers.py", line 1352, in _handle_status
    raise ValueError("Unknown status message: %r" % key)
ValueError: Unknown status message: 'KEY_CONSIDERED'

As this message is informational, but no action is required, this should not happen

Similar to #157