switch to promotion event for pipeline chaining

.drone.yml

@@ -31,12 +31,12 @@ steps:
       - echo $REGISTRY_PWD | docker login -u drone --password-stdin registry.jfmonty2.com
       - docker pull registry.jfmonty2.com/drone-server:latest
       - IMAGE_COMMIT_HASH=$(docker image inspect -f '{{ .Config.Labels.drone_commit_hash }}' registry.jfmonty2.com/drone-server:latest)
-      # compare
+      # compare and trigger CI if necessary
       - |
         if [[ $COMMIT_HASH != $IMAGE_COMMIT_HASH ]]; then
           echo 'Updates available, triggering build pipeline.'
           curl -X POST -H "Authorization: Bearer $DRONE_API_TOKEN" \
-          https://drone.jfmonty2.com/api/repos/jfmonty2/drone/builds
+          https://drone.jfmonty2.com/api/repos/jfmonty2/drone/builds/$DRONE_BUILD_NUMBER/promote?target=server-build
         else
           echo 'Image is already up to date.'
         fi
@@ -54,7 +54,9 @@ name: main
 
 trigger:
   event:
-    - custom
+    - promote
+  target:
+    - server-build
 
 steps:
   - name: prepare