Fixed typo with after_commit docs

Fixed syntax error on `after_commit` docs
Merge pull request #12648 from chrisledet/patch-1

Fixed typo with after_commit docs
Remove surprise if from show_exception middleware

This increase the readability within the rescue block.
Merge pull request #12655 from rails/ps-remove-surprise-if-in-show-exception-middleware

Remove surprise if from show_exception middleware
Make remote_ip detection properly handle private IPv6 addresses

Fixes #12638.