Preserves original whitespace on folded lines

[SergeyMosin]

This test fails:

test('headerLines preserves original whitespace on folded lines', async t => {
    const mail = `From: test@example.com
Subject: `+ "Hello\r\n    World" + `
Content-Type: text/plain

Body`;

    const email = await PostalMime.parse(mail);

    assert.strictEqual(email.subject, 'Hello    World');
});

Error:

✖ failing tests:

test at ---
✖ headerLines preserves original whitespace on folded lines (1.653798ms)

...

    generatedMessage: true,
    code: 'ERR_ASSERTION',
    actual: 'Hello World',
    expected: 'Hello    World',
    operator: 'strictEqual',
    diff: 'simple'