bump bbs
bump bbs

[finishes #118957301]

Submodule src/github.com/cloudfoundry-incubator/bbs 42d531e..ba40277:
  > fix a typo
  > BBS exits when master lock is lost

Signed-off-by: John Shahid <a20fa2b5347e8a5f4328621b7082b585e8d237c3@pivotal.io>

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