[Fix] Use short comments rather than long one

Rspamd fails to start with Lua-5.1 because long comment does not allow
nesting, see [1]. This change replaces it to short comments in order to
fix the issue but preserves this part as comment in docs.

[1] https://www.lua.org/manual/5.1/manual.html#7.1

Bug: https://bugs.gentoo.org/922522
Fixes: b189c9fea6 ("[Minor] lua_maps docs: apply formatting")
Fixes: https://github.com/rspamd/rspamd/issues/4784

lualib/lua_maps.lua

 --     optional = true,
 --   }
 -- }
+-- -- Then this function will look for opts.my_map parameter and try to replace it's with
+-- -- a map with the specific type, description but not failing if it was empty.
+-- -- It will also set options.my_map_orig to the original value defined in the map.
 --]]
 exports.fill_config_maps = function(mname, opts, map_defs)
   assert(type(opts) == 'table')