Clever "if let" assignment breaks in Swift 5.6.1 on Linux

[OurBigAdventure]

This clever little if statement in Cleaner.swift line 36:

if let headWhitelist, let dirtHead = dirtyDocument.head(), let cleanHead = clean.head() {

specifically changing it to:

if let headWhitelist = headWhitelist, let dirtHead = dirtyDocument.head(), let cleanHead = clean.head() {

would solve the issue.

[Aloisius]

For reference, the if let x {} shorthand for shadowing an optional was introduced in Swift 5.7.

Either the README need to be updated to note Swift 5.7 is required or this fixed.