tutorial.ipynb is incompatible with Python 3

[satsumas]

The introductory tutorial.ipynb should be runnable with Colab, but Colab defaults to Python 3 and tutorial.ipynb is in Python 2.

I have submitted some minor changes to make tutorial.ipynb run in Python 3:

#301

[mmitchef]

@satsumas thanks for leaving the changes but still it doesn't work and gave me this error "Cannot convert a symbolic Tensor (rotate/angles_to_projective_transforms/strided_slice_1:0) to a numpy array."