Bump src/cloud_controller_ng

Bump cloudfoundry/cloud_controller_ng:
  Matthew Sykes:
     Refactor AppObserver - Use the Backend abstraction ( Travis Unknown )
  Abhijit Hiremagalur:
     Add staging behavior to backends ( Travis Success: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/31731337 )

Signed-off-by: Peter Parente <pparent@us.ibm.com>