bump garden-linux
bump garden-linux

[finishes #104711118]

Submodule src/github.com/cloudfoundry-incubator/garden-linux 2d6ecc1..a02bfcc:
  > Avoid running test on Darwin which fails on El Capitan

Signed-off-by: Glyn Normington <94963367bb5bbf046ec526f1d42ce35228051963@pivotal.io>

cloudfoundry-incubator/garden-linux-release,cloudfoundry-incubator/garden-linux-release,cloudfoundry-incubator/garden-linux-release,cloudfoundry-incubator/garden-linux-release,cloudfoundry-incubator/garden-linux-release