bump vizzini
bump vizzini

Submodule src/code.cloudfoundry.org/vizzini d50dcf7b..0764d1bf:
  > Update the grace sha1sum

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

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