bump locket
bump locket

Submodule src/code.cloudfoundry.org/locket 42257af..8ebe6ec:
  > add more logging to the metrics notifier
  > fix some race condition in locket_test

Signed-off-by: John Shahid <d5f6a919b5b5e6a4f7f09f1adf45e90e5c38b58e@gmail.com>

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