add support for lua 5.2, 5.3 and above

[paulo-erichsen]

orbit works in lua 5.1.5, but is broken in 5.2 and above (such as 5.2.4 and 5.3.5)

when I try to use orbit in 5.2, an exception is thrown

lua: /usr/share/lua/5.3/orbit.lua:9: attempt to call a nil value (local 'setfenv')
stack traceback:
    /usr/share/lua/5.3/orbit.lua:9: in main chunk
    [C]: in function 'require'
...

the line of code in question is

9: setfenv(1, _G)

related info:

• https://leafo.net/guides/setfenv-in-lua52-and-above.html
• https://stackoverflow.com/a/14290609
• https://github.com/luaposix/luaposix/issues/299
• https://www.corsix.org/content/look-lua-52-work3