Add LUA linting

.drone.yml

@@ -19,7 +19,7 @@ steps:
     - apk add --no-cache build-base curl unzip
     - apk add --no-cache lua5.1 lua5.1-dev luarocks5.1
     - luarocks-5.1 install luacheck
-    - luacheck sources --allow-defined
+    - luacheck sources/*.lua --compat --allow-defined --no-unused-args
 
 - name: build
   image: alpine