Bump src/cloud_controller_ng

Bump cloudfoundry/cloud_controller_ng:
  Chris Adams:
     Disallow setting an app to zero instances ( Travis started: https://travis-ci.org/cloudfoundry/cloud_controller_ng/builds/22135215 )

[delivers #61926402]

Signed-off-by: Eric Malm <emalm@pivotallabs.com>