Add a value to the arrays duplicates test array.

Hi!

First, I want to say thank you _so much_ for putting this together. I am just starting to learn JavaScript and this has been really helpful!

I noticed that the "duplicates" test in arrays had only pairs of duplicates, which let me get away with using a pair of nested for loops. I added another "3" to the test array to prompt people to think about other ways to do this.

This test still passes with your answer in js-assessment-answers so there's no pull request necessary over there.

Thanks again! Have a great weekend.
Matt