initialize unicorn_bin and gunicorn_bin for Herder object

this is a commit i accidentally omitted which breaks the -b and -g flags

the checks at
 https://github.com/ewdurbin/unicornherder/blob/72bc15d8833f327a2a247b8361b01f76b26d328e/unicornherder/herder.py#L104
  and https://github.com/ewdurbin/unicornherder/blob/72bc15d8833f327a2a247b8361b01f76b26d328e/unicornherder/herder.py#L107

need these attributes. sorry.