[lua/*] Update links to Lua Short Reference

[plavin]

The en and es-es Lua pages both point to a page on lua-users.org that contains broken links to luarefv51.pdf. The fr-fr version contains a broken link. The other languages contain a different link. I have updated these 3 files to point to the same version the other Lua pages point to.

I attempted to edit lua-users.org but it appears that site is broken. It may be wise to change all lua-users.org links to archive.org links if that website is unmaintained.

For reference, here is a link to an archive version of Lua Short Reference page.

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