lua: fix license path for lua 5.2

The file containing the license for lua 5.1 was removed and the license
text was added to the readme in 5.2.

[Peter: swap 5.1/5.2 logic]
Signed-off-by: Frank Hunleth <fhunleth@troodon-software.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>