At present, luasandbox is tied to Lua 5.1, which is so out of date that certain features of Lua 5.2 are backported to luasandbox's implementation of Lua.
Perhaps it is time to move on.
To begin with, references to Lua version hardcoded into luasandbox source code could be removed and made configurable in the options for cmake or ./configure (defaulting to Lua 5.1).
The hardcoded Lua version is found in config.cmake and config.m4. The file FindLua51cpp.cmake ought to be, I guess, cloned into FindLua52cpp.cmake and FindLua53cpp.cmake or parametrised somehow.