.travis.yml: Update golang, helm and k8s versions (#6)

* Add golang 1.11
* Update kubectl from 1.9.6 to 1.11.3
* Update helm from 2.8.2 to 2.11.0

Author: mrueg

.travis.yml

@@ -3,7 +3,8 @@ matrix:
     - language: go
       go:
         - 1.9
-        - "1.10"
+        - 1.10
+        - 1.11
         - tip
       install:
         - go get -u github.com/golang/lint/golint
@@ -20,8 +21,8 @@ matrix:
 
     - language: generic
       env:
-        - KUBECTL_VERSION=v1.9.6
-        - HELM_VERSION=v2.8.2
+        - KUBECTL_VERSION=v1.11.3
+        - HELM_VERSION=v2.11.0
       install:
         - wget https://storage.googleapis.com/kubernetes-release/release/${KUBECTL_VERSION}/bin/linux/amd64/kubectl -O /tmp/kubectl
         - chmod +x /tmp/kubectl