Make 2d-projection-of-3d-surface Python 3 compatible.

[jonmmease]

Tutorial: https://plot.ly/python/2d-projection-of-3d-surface/

See: plotly/plotly.py#937

Problem: I think the problem is this line: ztickvals=range(-6,4). In Python 2 this results in a serializable list, in Python 3 it's a non-serializable range object.