Fixing UnicodeDecodeError & updating Django requirement

I hit a bug in django-jenkins when the traceback contains unicode characters, ie:

  File "[...]/workspace/env/local/lib/python2.7/site-packages/django_jenkins/runner.py", line 122, in _add_tb_to_test
    test_result.set('message', str(exc_value))
UnicodeEncodeError: 'ascii' codec can't encode characters in position 148-156: ordinal not in range(128)

This trivial PR solves the problem. While I was at it I updated the requirements to avoid require.io showing the scary insecure-button.