[dev-context] CGModules update: Letter module version 2021.10.16 published.

Wolfgang Schuster submitted an update to the Letter module package. Version number: 2021.10.16 License type: GNU General Public License Wants to be in ConTeXt distribution: no Wants to be synced with CTAN: no Summary description: Writing letters with ConTeXt. Announcement text: ---------------------------------------------------------------------- Fixes a typo in the memo module which caused an error. ----------------------------------------------------------------------