fix ci

.gitlab-ci.yml

@@ -15,8 +15,8 @@ build:
       - dist
   script:
     - apk add --no-cache imagemagick pkgconfig imagemagick-dev gcc libc-dev
-    - mkdir previews
-    - mkdir dist
+    - rm -rf previews && mkdir -p previews
+    - rm -rf dist && mkdir -p dist
     - go run main.go
     - mv index.html dist/
     - mv previews/ dist/