Use newer trigger syntax

.drone.yml

@@ -1,22 +1,13 @@
 ---
 kind: pipeline
-
 name: default
-
 steps:
-  - name: Build Minio docker image
-    image: docker:stable
-    volumes:
-      - name: docker_sock
-        path: /var/run/docker.sock
-    commands:
-      - docker build --no-cache -t autonomic/minio:drone .
-
   - name: Deploy Minio with Dokku
     image: appleboy/drone-git-push:0.2.0-linux-amd64
     settings:
       remote: ssh://dokku@minio.autonomic.zone:222/minio
       ssh_key:
         from_secret: drone_deploy_key
-    when:
-      branch: master
+    trigger:
+      branch:
+        - master