Bump src/dea_next

Bump cloudfoundry/dea_ng:
  Julian Friedman:
     instances.json does not forget about instances in stopping state ( Travis Success: https://travis-ci.org/cloudfoundry/dea_ng/builds/30762955 )
  Graeme Davison and Joseph Palermo:
     Add code coverage reporting ( Travis Success: https://travis-ci.org/cloudfoundry/dea_ng/builds/30503176 )

Signed-off-by: Matthew Sykes <matthew.sykes@gmail.com>