Bump Helm version in Auto-DevOps.gitlab-ci.yml

See https://github.com/helm/helm/releases/tag/v2.14.0
for upstream changelog

changelogs/unreleased/bump-auto-devops-helm-2-14-0.yml

+---
+title: Bump Helm version in Auto-DevOps.gitlab-ci.yml to 2.14.0
+merge_request: 28527
+author:
+type: other

lib/gitlab/ci/templates/Auto-DevOps.gitlab-ci.yml

@@ -51,7 +51,7 @@ variables:
   POSTGRES_VERSION: 9.6.2
 
   KUBERNETES_VERSION: 1.11.10
-  HELM_VERSION: 2.13.1
+  HELM_VERSION: 2.14.0
 
   DOCKER_DRIVER: overlay2