🚑 Fix doc CI generation

.gitlab-ci.yml

 pages:
-  image: jimho/lua
+  image: abaez/luarocks
   stage: deploy
   script:
+    - luarocks install penlight
     - curl -L https://github.com/stevedonovan/LDoc/tarball/master > master.tgz
     - tar xzf master.tgz
-    - lua LDoc-master/ldoc.lua .
+    - lua stevedonovan-LDoc*/ldoc.lua .
   artifacts:
     paths:
       - public