Exception when a user has no name

[jayvdb]

On https://github.com/coala/gh-board, the following all cause an exception:

{'user_name': 'domlobo', 'name': None}
{'user_name': 'greenkeeper[bot]', 'name': None}
{'user_name': 'brentirwin', 'name': None}
{'user_name': 'adjohnson916', 'name': None}
{'user_name': 'domlobo', 'name': None}
{'user_name': 'brentirwin', 'name': None}
{'user_name': 'ANURADHAJHA99', 'name': None}

All Contributors:
Traceback (most recent call last):
  File "/home/jayvdb/.local/bin/octohatrack", line 11, in <module>
    load_entry_point('octohatrack', 'console_scripts', 'octohatrack')()
  File "/home/jayvdb/projects/ghuser/octohatrack/octohatrack/__main__.py", line 53, in main
    display_results(repo_name, contributors, len(api))
  File "/home/jayvdb/projects/ghuser/octohatrack/octohatrack/helpers.py", line 16, in display_results
    for user in sorted(contributors, key=lambda k: k['name'].lower()):
  File "/home/jayvdb/projects/ghuser/octohatrack/octohatrack/helpers.py", line 16, in <lambda>
    for user in sorted(contributors, key=lambda k: k['name'].lower()):
AttributeError: 'NoneType' object has no attribute 'lower'