[Minor] Update experiment name to include timestamp so that experiments are sorted in places like file systems.

[eihli]

This is a really small issue. I think it would be nice if I could quickly and easily determine which of my training runs was the most recent training run. See the screenshot below. I've got 9 training runs in my model output directory (shown when I tab-complete in ZSH) and I have no idea which is the most recent.

[nomitchell]

I added a pull request to update the model saved name from a random id to the current time in timestamp format y-m-d_h:m:s