Use a different image for rsync

If this works, there’s no need to install rsync separately. There isn’t anything
in this step that has anything to do with Emacs, so it should work.

.gitlab-ci.yml

@@ -184,10 +184,10 @@ package:
 
 deploy:
   stage: deploy
+  image: instrumentisto/rsync-ssh
   dependencies:
     - package
   before_script:
     - chmod 600 "$DEPLOY_KEY"
-    - apk update && apk add rsync
   script:
     - rsync -e "ssh -o \"UserKnownHostsFile $KNOWN_HOSTS\" -p 4511 -i $DEPLOY_KEY" -v -c -r --delete bin/ "elpa@ryuslash.org:"