models/run directory name incompatible with Windows

[jrao1]

This makes it impossible to checkout the project under Windows. I would suggest removing "-" and ":" from the directory name and change line 336 of wavenet.py to

run_dir = os.path.join('models', datetime.datetime.now().strftime('run_%Y%m%d_%H%M%S'))

[basveeling]

Thanks for the tip! Let me know if the last fix works, and if you run into any other problems on windows.