Week 3 - Exercise 6 - compute_cost, getting incorrect mean cost

[paulinpaloalto]

Great! There are 3 popular errors on that code block:

1. Reversing the arguments.
2. Forgetting the transposes.
3. Forgetting the from_logits = True argument.

Or some combination of the above. Each mistake gives a characteristic wrong answer, but the combinations can be a little harder to diagnose.