[tldoc] Lua 5.3, not LuaTeX 5.3

[Karl Berry]

A sharp-eyed reader (Juergen Fenn, thanks Juergen) pointed out that my
news item about "Lua\TeX\ 5.3" should be "Lua 5.3":

-Lua\TeX: Preparation for moving to Lua\TeX\ 5.3 in 2019: a binary
+Lua\TeX: Preparation for moving to Lua 5.3 in 2019: a binary

Clearly it's not the end of the world if this tweak isn't made
everywhere, but if you feel like doing it, go for it.  I've changed the
English and Italian (since I just compiled the Italian anyway).
(Zofia, I tested changing the Polish too but my resulting html/pdf were
very different from yours; sorry.)

I hope there won't be any more, but who knows :( ... --thanks, karl.