Don't error out when there are pinned formula, we don't want to upgrade
those, so skipping them is perfectly fine!
See https://github.com/Homebrew/brew/issues/4063:
"brew upgrade reports "Error" for pinned packages"
brew outdated --verbose || ax_abort "Failed to list outdated packages!"
echo
- brew upgrade --cleanup || ax_abort "Upgrade failed!"
+ brew upgrade --ignore-pinned --cleanup || ax_abort "Upgrade failed!"
echo
ax_msg - "Cleaning up ..."