Bump src/stager

Bump cloudfoundry-incubator/stager:
  Momchil Atanasov:
     Update deps ( Travis Success: https://travis-ci.org/cloudfoundry-incubator/stager/builds/25193400 )
     Stop using nats queues ( Travis Unknown )
     Clean up stager test ( Travis Unknown )
     Refactor inbox test ( Travis Success: https://travis-ci.org/cloudfoundry-incubator/stager/builds/25181231 )
  Alex Suraci:
     forward detected start command to CC ( Travis Success: https://travis-ci.org/cloudfoundry-incubator/stager/builds/25183324 )
     deps ( Travis Unknown )