fix(ci): correct image for generating slate docs

.woodpecker/docs.yml

@@ -22,10 +22,11 @@ pipeline:
 
   slate-docs:
     image: 'slatedocs/slate'
+    pull: true
     group: 'generate'
     commands:
       - cd docs/api
-      - bundle exec middleman build --clean
+      - bundle exec middleman build --clean --watcher-disable
 
   archive:
     image: 'alpine'