Bump src/loggregator

Bump :
  Alex Jackson:
     switch to use https instead of git protocol for submodule
     update diagram to make it clear that syslog drain output comes from the loggregator server not the traffic controller
  John Tuley:
     Un-flake tests
     Upgrade ginkgo/gomega
     [#72348402] continue listening to stdout/stderr sockets on error

Signed-off-by: Alex Jackson <ajackson@pivotallabs.com>