Add bump-formula-pr to Brew update steps
Add bump-formula-pr to Brew update steps

This commit updates the Brew Formula update steps to include the
`bump-formula-pr` command for use with simple version bumps.

Signed-off-by: John McCabe <a51dda7c7ff50b61eaea0444371f4a6a9301e501@johnmccabe.net>

itscaro/faas-cli,itscaro/faas-cli,itscaro/faas-cli