chore(rootfs/Dockerfile): update helm to v2.13.1 (#162)

See https://github.com/helm/helm/releases/tag/v2.13.1

Author: mboersma

rootfs/Dockerfile

@@ -7,7 +7,7 @@ ENV AZCLI_VERSION=2.0.60 \
     GO_VERSION=1.12.1 \
     GLIDE_VERSION=v0.13.2 \
     GLIDE_HOME=/root \
-    HELM_VERSION=v2.13.0 \
+    HELM_VERSION=v2.13.1 \
     KUBECTL_VERSION=v1.10.13 \
     ETCDCTL_VERSION=v3.1.8 \
     GOLANGCI_LINT_VERSION=v1.16.0 \