Update Docker build layer to go 1.11.13

[LucasRoesler]

Per the security announcement https://groups.google.com/forum/#!topic/golang-announce/65QixT3tcmg we should update the docker build layers to at least Go 1.11.13

Possible Solution

The builder layer in the Dockerfile should use golang:1.11

Related

Update Dockerfile and rebuild/release

openfaas/faas#1291
openfaas/templates#170
openfaas/faas-netes#494
openfaas/nats-queue-worker#66
openfaas/of-watchdog#78
https://github.com/openfaas-incubator/faas-idler/issues/32
openfaas/golang-http-template#28
#4
openfaas-incubator/vcenter-connector#27
openfaas-incubator/faas-memory#3
openfaas-incubator/faas-rancher#8

Only Rebuild

openfaas/faas-swarm#56
openfaas/ingress-operator#10
https://github.com/openfaas-incubator/openfaas-operator/issues/87

[alexellis]

@ewilde PTAL