Update vae_example.ipynb

[tayfununal]

I guess, D has forgotten in the equation.

[jmtomczak]

No, this is not correct because log_var is of size mini_batch x D. When we calculate log_p , we treat all variables as tensors. Adding D as you suggest would result in scaling log_var which would be incorrect.
However, I spotted a different mistake. The constant shouldn't have D. I am going to correct it.