Write a function `log_prior` that takes a numpy array `train_labels` as input, and outputs the following vector as a column numpy array (i.e., with shape $(2,1).

log pᵧ = [ log p(y = 0) ]
[ log p(y = 1) ]

Try and avoid the utilization of loops as much as possible. No loops are necessary.
Hint: Make sure all the array shapes are what you need and expect. You can reshape any numpy array without any tangible computational over-head.