Requires LUA 5.3

[hi-flyer]

First, thank you for the software. it works well (at least sha256) I had to upgrade Ubuntu 18.04 version of IMAPFILTER to accommodate LUA 5.3 but having done that it worked great.

not really a big deal as I figured it out but you should note that the code requires LUA 5.3 or I guess higher to work in the dependancies sections on the README. Ubuntu 18.04 defaults to LUA 5.2 as preferred. don't know yet on Ubuntu 20.04