Update deprecated assertEquals to assertEqual

[bev-a-tron]

Replace deprecated assertEquals with assertEqual. Running through the koans one by one, I got this error message on koans/about_iteration.py:

You have not yet reached enlightenment ...
  AttributeError: 'AboutIteration' object has no attribute 'assertEquals'. Did you mean: 'assertEqual'?

I checked that the koans still run normally after the fix.