fix(ci): correct image for generating slate docs

.woodpecker/docs.yml

@@ -24,11 +24,12 @@ pipeline:
     image: 'slatedocs/slate'
     group: 'generate'
     # Slate requires a specific directory to run in
+    directory: '/srv/slate'
     commands:
+      - echo "$PWD"
       - mv "$CI_WORKSPACE/docs/api" /srv/slate/source
-      - cd /srv/slate
-      - /srv/slate/slate.sh build
-      - mv /srv/slate/build "$CI_WORKSPACE/docs/api-build"
+      - bundle exec middleman build --clean --watcher-disable
+      - mv build "$CI_WORKSPACE/docs/api-build"
 
   archive:
     image: 'alpine'