lua_api.html: Fix page root

lua_api.html

@@ -1,6 +1,7 @@
 ---
 title: Lua Modding API Reference
 layout: default
+root: .
 ---
 <div class='notice'>
 <h2>This is lua_api.txt nicely formated: I did not write this</h2>
@@ -6951,4 +6952,4 @@ minetest.spawn_tree(pos,apple_tree)
 --  ^ Returns an iterator (use with `for` loops) for all player names
 --  ^ currently in the auth database.
 }
-</code></pre>
+</code></pre>