Bump src/gorouter/src/github.com/cloudfoundry/gorouter

Bump cloudfoundry/gorouter:
  Eric Malm:
     Revert "Remove old copy of server.go and use the library" ( Travis Success: https://travis-ci.org/cloudfoundry/gorouter/builds/15800611 )
  Ruth Byers:
     Fix flakey test when using yagnats ( Travis Success: https://travis-ci.org/cloudfoundry/gorouter/builds/15561182 )

Signed-off-by: Eric Malm <emalm@pivotallabs.com>