bump bbs
bump bbs

Submodule src/code.cloudfoundry.org/bbs 6f30f7a69..9ebaacf8e:
  > fix required protoc version in README

cloudfoundry-incubator/diego-release,cloudfoundry-incubator/diego-release,cloudfoundry-incubator/diego-release,cloudfoundry-incubator/diego-release