SKIP UPDATE CHECK: Update Envoyfilter
Skip update check so it doesn't mad about the readme.
The changes here make use of the 4th param for string.find - http://www.lua.org/manual/5.2/manual.html#pdf-string.find
A value of true as a fourth, optional argument plain turns off the pattern matching facilities, so the function does a plain "find substring" operation, with no characters in pattern being considered magic. Note that if plain is given, then init must be given as well.
This makes sure that magic characters don't get interpreted as magic (specifically we are concerned about the hyphen).