Variables and Operators lesson: Fix link from one of the Knowledge Check

[LevoratoJoao]

Because

One of the links from Knowledge check at Variables and Operators was wrong, [Explain the difference between == and ===.] had the same link as [When would you receive a NaN result?]

This PR

This PR changed the link of [Explain the difference between == and ===.] to https://www.w3schools.com/js/js_operators.asp

Additional Information

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[JoshDevHub]

Nice find! Thank you for contributing.