bump healthcheck
bump healthcheck

[finishes #152000076]

Submodule src/code.cloudfoundry.org/healthcheck 4b22520e..ab5f862d:
  > add X-Forwarded-Proto header to http healthcheck requests

Signed-off-by: Danny Cao <5ffc8b7cff3b9f2acb630fd157ff837ced3278ae@us.ibm.com>

cloudfoundry-incubator/diego-release,cloudfoundry-incubator/diego-release,cloudfoundry-incubator/diego-release,cloudfoundry-incubator/diego-release