There are a few errors in the god mode script.

1. For on @p /heal is applied to the sender not the player being set to god mode
2. For off @p there is a typo in the god mode argument resulting in it not turning off
3. For on /heal is not applied due to it the sender of /heal being console.

I am preparing a pull request that fixes these 3 issues.

Good job noticing and fixing this!