Fix sample configuration logging.yaml work in python3

[ghost]

In Python3 with PyYAML, logging.config.dictConfig sample not working, got errors as follows:

Traceback (most recent call last):
  File "test.py", line 7, in <module>
    logging.config.dictConfig(conf['logging'])
  File "/Users/takashibagura/.pyenv/versions/3.5.0/lib/python3.5/logging/config.py", line 795, in dictConfig
    dictConfigClass(config).configure()
  File "/Users/takashibagura/.pyenv/versions/3.5.0/lib/python3.5/logging/config.py", line 556, in configure
    for name in sorted(handlers):
TypeError: unorderable types: str() < NoneType()

I was changed the key of handlers is not to None.

[coveralls]

Coverage remained the same at 89.08% when pulling 0b2bad6 on takashibagura:master into c590560 on fluent:master.

[repeatedly]

Thanks for the patch!