Update .gitlab-ci.yml file fix path for index file

.gitlab-ci.yml

@@ -24,7 +24,7 @@ pandoc:
     entrypoint: ["/bin/sh", "-c"]
   script:
     - pandoc --standalone topics/topic-template.md -o build/topic-template.html  --mathjax
-    - pandoc --standalone build/index.md -o index.html --mathjax
+    - pandoc --standalone build/index.md -o build/index.html --mathjax
   artifacts:
     paths:
       - build/*.html