SnowboyDetect will not take unicode strings in Python 3

[jacobtomlinson]

When starting up in Python 3 the following traceback happens because the model path is being passed as a unicode string. It needs to be passed as an old fashioned string.

Traceback (most recent call last):
  File "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/python3.5/runpy.py", line 170, in _run_module_as_main
    "__main__", mod_spec)
  File "/usr/local/Cellar/python3/3.5.1/Frameworks/Python.framework/Versions/3.5/lib/python3.5/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/Users/jacob/Projects/opsdroid/opsdroid-audio/opsdroidaudio/__main__.py", line 243, in <module>
    main()
  File "/Users/jacob/Projects/opsdroid/opsdroid-audio/opsdroidaudio/__main__.py", line 239, in main
    oaudio.start()
  File "/Users/jacob/Projects/opsdroid/opsdroid-audio/opsdroidaudio/__main__.py", line 52, in start
    self.detector = audio.HotwordDetector(self.model, sensitivity=0.4)
  File "/Users/jacob/Projects/opsdroid/opsdroid-audio/opsdroidaudio/audio.py", line 117, in __init__
    model_str=model_str.encode())
  File "/Users/jacob/Projects/opsdroid/opsdroid-audio/snowboydetect/snowboydetect.py", line 101, in __init__
    this = _snowboydetect.new_SnowboyDetect(resource_filename, model_str)
TypeError: in method 'new_SnowboyDetect', argument 1 of type 'std::string const &'