Update Chapter 6's vestigial "previous chapter" references to Chapter 4 #272

	name: Run PR Tests

	on:
	pull_request:
	push:
	branches: [master]

	jobs:
	build:
	runs-on: ubuntu-latest

	steps:
	- uses: actions/checkout@v2

	- name: Set up PureScript toolchain
	uses: purescript-contrib/setup-purescript@main

	- name: Cache PureScript dependencies
	uses: actions/cache@v2
	with:
	key: ${{ runner.os }}-spago-${{ hashFiles('*/.dhall') }}
	path: \|
	exercises/*/.spago
	exercises/*/output

	- name: Set up Node toolchain
	uses: actions/setup-node@v1
	with:
	node-version: "14.x"

	- name: Cache NPM dependencies
	uses: actions/cache@v2
	env:
	cache-name: cache-node-modules
	with:
	path: ~/.npm
	key: ${{ runner.os }}-build-${{ env.cache-name }}-${{ hashFiles('**/package.json') }}
	restore-keys: \|
	${{ runner.os }}-build-${{ env.cache-name }}-
	${{ runner.os }}-build-
	${{ runner.os }}-

	- name: Install NPM dependencies
	run: npm install purescript spago markdownlint-cli@0.37.0

	- name: Run Build
	run: ./scripts/buildAll.sh

	- name: Run tests
	run: ./scripts/testAll.sh

	- name: Prepare exercises
	run: ./scripts/prepareExercises.sh

	- name: Run tests again
	run: ./scripts/testAll.sh

	- name: Run Markdown lint
	run: npx markdownlint */.md

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