• Update to 1.2.1
• Change LICENSE since support has been added for "or later" variants of GNU licenses
• Add LICENSE_FILE

Changelog:

https://github.com/baedert/corebird/releases/tag/1.2.1

Reviewed by: amdmi3, junovitch (mentors)
Approved by: amdmi3, junovitch (mentors)
Differential Revision: D6322