The plugin does not exist. Run `snapcraft list-plugins` to see the available plugins.
Traceback (most recent call last):
  File "./snapcraft/scripts/generate_reference.py", line 115, in <module>
    main()
  File "./snapcraft/scripts/generate_reference.py", line 111, in main
    Reference(args.output_file)
  File "./snapcraft/scripts/generate_reference.py", line 54, in __init__
    self._read()
  File "./snapcraft/scripts/generate_reference.py", line 62, in _read
    text = _get_help_output(topic)
  File "./snapcraft/scripts/generate_reference.py", line 32, in _get_help_output
    return _run_snapcraft(['help', topic], lines)
  File "./snapcraft/scripts/generate_reference.py", line 38, in _run_snapcraft
    cmd, cwd=os.path.join(os.path.dirname(__file__), '../../bin'))
  File "/usr/lib/python3.4/subprocess.py", line 620, in check_output
    raise CalledProcessError(retcode, process.args, output=output)
subprocess.CalledProcessError: Command '['./snapcraft', 'help', 'kernel']' returned non-zero exit status 1