Makefile.setup.inc: do not include trailing slash in LUADIR
Makefile.setup.inc: do not include trailing slash in LUADIR

LUADIR is used with a following slash everywhere, and it looks confusing
when seeing "//" during the build.

keplerproject/luarocks,keplerproject/luarocks,luarocks/luarocks,tarantool/luarocks,luarocks/luarocks,tarantool/luarocks,keplerproject/luarocks,keplerproject/luarocks,luarocks/luarocks,tarantool/luarocks