fix(junit): fix locale sensitivity with junit

[JonnyPower]

closes #323

What does this PR do?

Changes the start date format util to follow predictable ISO standard

What issues does this PR fix or reference?

#323

Functionality Before

Test summary start date was in use locale

Functionality After

Test summary start date is in ISO format so can be used programmatically later by junit reporter

[JonnyPower]

can replicate with this test in junitReporter.test.ts;

  it('should format start time with different locale', () => {
    const modified = { ...testResults };
    modified.summary.testStartTime = `${new Date().toDateString()} ${new Date().toLocaleTimeString(
      'en-CA'
    )}`;
    expect(modified.summary.testStartTime).to.contain('.m.');
    reporter.format(modified);
  });

[shetzel]

We should be able to close this since #334 was merged. Thanks for your hard work and patience with this @JonnyPower !