normalised lua doc to 80 chars per line

When this was originally written, it was written for a line-width of 50
characters, however Learn X in Y Minutes' site is designed for
80-character widths. This made it look very out of place.
Merge pull request #555 from iirelu/lua-linewidth-80

[lua/en] Normalised Lua's doc to a width of 80 characters