Update lua module to 0.9.7

Signed-off-by: Lance Chen <cyen0312@gmail.com>
Force to build against luajit

Build will fail if lua 5.2 is installed.
Use LUAJIT_LIB and LUAJIT_INC to force nginx
build against luajit.

Signed-off-by: Lance Chen <cyen0312@gmail.com>