message: Spell banner properly.
diff: /**
  * Each announcement must have a unique `storageKey` to ensure people who
  - * dismiss announcement A will see a new banenr for announcement B.
  + * dismiss announcement A will see a new banner for announcement B.
  * For simplicity, the announcement `storageKey` is the date the announcement
  * was made, in the `yyyy-mm-dd` format.
  */
  