Simplify as much as possible

.drone.yml

@@ -1,22 +1,5 @@
 pipeline:
-  restore-cache:
-    image: drillster/drone-volume-cache
-    restore: true
-    mount:
-      - /drone/.bundle
-    volumes:
-      - /tmp/bundle-cache:/cache
   build:
-    image: ruby:2.5.1-alpine3.7
-    environment:
-      - BUNDLE_PATH=/drone/.bundle
+    image: jekyll/jekyll:latest
     commands:
-      - bundle install
-      - bundle exec jekyll build
-  rebuild-cache:
-    image: drillster/drone-volume-cache
-    rebuild: true
-    mount:
-      - /drone/.bundle
-    volumes:
-      - /tmp/bundle-cache:/cache
+      - jekyll build