Fix ECONNREFUSED error when running the /api/preview tests

[chasenlehara]

Slack thread for context: https://cali.slack.com/archives/C069V9TTN/p1639757244068800

Steps to reproduce:

1. Remove the .skip from a preview test, e.g.

   a2jdat/test/routes/preview.js

   Lines 29 to 30 in 6f59824

   	// TODO: this test is skipped due to the issue described in https://github.com/CCALI/a2jdat/issues/100
   	it.skip('previews basic templates correctly', function (done) {

2. Run the tests (npm test)

Expected results: tests would pass.

Actual results: all the tests pass except this preview test.

Note that if you skip this test, then the preview test will pass:

a2jdat/test/routes/assemble.js

Lines 26 to 42 in 6f59824

	it('assembles basic templates correctly', function (done) {
	// Set a longer timeout, otherwise the PDF generation will fail
	this.timeout(5000)
	const fileDataUrl = path.join(__dirname, '..', 'data', 'DEV', 'guides', 'Guide1262')
	request(app)
	.post('/api/assemble')
	.send({
	answers: '{}',
	fileDataUrl
	})
	.expect(200)
	.end(function (err) {
	if (err) return done(err)
	done()
	})
	})

What I observed with @tobiasnteireho is that when a document is rendered with SSR for assembly or preview, it works the first time, but subsequent calls fail because the server has been torn down.

I am happy to pair with whoever picks this up so I can help them reproduce it.