Log Message:
Update ruby-mixlib-log to 1.7.1.

1.7.1 (2016-08-12)

* Allow applications to query if they've got loggers #18 (thommay)

1.7.0 (2016-08-04)

* test with updated ruby versions and run cucumber #16 (thommay)
* Add dev dependency on chefstyle #15 (tas50)
* Misc cleanup + add Travis #14 (tas50)
* File log devices opened by mixlib-log should be closed. #13 (mhorbul)
* Include the license type in the .gemspec #9 (benders)
* MIXLIB-10: don't be so pessimistic about development libraries #8 (jkeiser)

Fixed bugs:

* Ensure that arguments to Mixlib::Log#add are passed as is to all loggers #7
  (ketan)
* Fixing RDoc formatting of README.rdoc. #4 (ampledata)