fix(ci): override alpine/helm entrypoint so shell wrapper runs

The alpine/helm:4.1 image has 'helm' as ENTRYPOINT. GitLab CI wraps
step_script in sh, which the container resolves to 'helm sh ...',
failing with 'unknown command sh for helm'. Setting entrypoint: [""]
lets GitLab's sh wrapper execute normally before invoking helm.

.gitlab-ci.yml

@@ -26,7 +26,9 @@ backend:docker:
 
 backend:deploy:
   stage: deploy
-  image: alpine/helm:4.1
+  image:
+    name: alpine/helm:4.1
+    entrypoint: [""]
   before_script:
     - mkdir -p ~/.kube
     - echo "$KUBECONFIG_DATA" > ~/.kube/config
@@ -74,7 +76,9 @@ web:docker:
 
 web:deploy:
   stage: deploy
-  image: alpine/helm:4.1
+  image:
+    name: alpine/helm:4.1
+    entrypoint: [""]
   before_script:
     - mkdir -p ~/.kube
     - echo "$KUBECONFIG_DATA" > ~/.kube/config