lightning_mnist_tpu crashes
🐛 Bug

To Reproduce
Run https://colab.research.google.com/drive/1-_LKx4HwAxl5M6xPJmqAAu444LTDQoa3 with VERSION = "1.5"
There were other error when trying to run with other versions from ["1.5" , "20200325", "nightly"] neither of them seem to work properly, there's always some sort of bug that pops up.
at this one moment when i had finally got it to run the model, the second time i ran the cell, it crashed, could be that i had to free up mem. but i dont see why it shouldn't have been done automatically.