Bump linux-circus

[delivers #79480586]

Bump cloudfoundry-incubator/linux-circus:
  Jacques Chester and Rick Reilly:
     Begone, comment (aka Extract Variable) ( Travis Success: https://travis-ci.org/cloudfoundry-incubator/linux-circus/builds/36197768 )
     Ensure Procfile web: lines dominate buildpack /bin/release output at runtime ( Travis Success: https://travis-ci.org/cloudfoundry-incubator/linux-circus/builds/36196239 )