bump benchmarkbbs
bump benchmarkbbs

Submodule src/code.cloudfoundry.org/benchmarkbbs a61f7847..fec30a47:
  > use durationjson for time.Duration JSON logic

Signed-off-by: Genevieve LEsperance <1b6a7b865633211adcfeed81fa254bd2ba36f0db@pivotal.io>

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