Bump src/linux-circus

Bump cloudfoundry-incubator/linux-circus:
  Max Brunsfeld:
     Log both healthcheck messages to stdout ( Travis started: https://travis-ci.org/cloudfoundry-incubator/linux-circus/builds/30000046 )
     Merge pull request #6 from cloudfoundry-incubator/healthcheck-logging ( Travis Success: https://travis-ci.org/cloudfoundry-incubator/linux-circus/builds/29999650 )
  Amit Kumar Gupta:
     Improve healthcheck logging [#74744868] ( Travis Success: https://travis-ci.org/cloudfoundry-incubator/linux-circus/builds/29930720 )