Homebrew package is updated to the version 0.12.2.
"This is a soft-fork and an update to Hard Fork 12 to address oversized blocks and transactions. All witnesses should update as soon as possible."
To update your installation you need to:
Step 1: Update Homebrew:
brew update
Step 2: Reinstall existing Steem installation:
brew reinstall steem
PS: If you don't have Steem installed, just use the following command:
brew install TigerND/core/steem