Use `set -e` to fail fast

Hi, I just got started to use mina today. And I noticed that even if some command when deploying exits with a non-zero status, the following commands would still execute. I really don't want that to happen since I simply don't want to know what would happen in that situation.

This patch makes use of bash's `-e` option and bail out asap if any command goes bad. Jenkins CI uses this. And I think deploying scripts are even more critical than CI scripts.

Hope it gets merged :)