Add check for master changes

This can abort the whole pipeline, because releases also show up as a commit.

.drone.yml

@@ -5,6 +5,12 @@ name: default
 
 steps:
 
+- name: Check for changes in master branch
+  image: alpine
+  commands:
+    - apk update && apk add bash curl grep jq sed
+    - ./check-master-for-changes.sh
+
 - name: Build & Publish Development Image
   image: plugins/docker
   settings: