Fix arrayPop function

[amoradi]

There is currently a method called arrayPop that lives in /lib/arrayPop.js.
It is incomplete and needs to be fixed!

arrayPop pops off the last item in Array (Strings are viable too) without mutating it. Pass the mutate param as true to mutate.

Acceptance Criteria:

1. Running yarn test arrayPop results in tests passing.
2. You have written a skeleton method for someone else to work on.
3. You have written tests surrounding your skeleton method.
4. Running yarn lint does not print any errors to the console!
5. Optional: write one or two more tests surrounding the method you are solving to account for potential edge cases.

Please include the skeleton of a new method + an accompanying test for someone else to work on at the time of creating a pull request! A pull request will most likely be denied if it does not contain a skeleton method for someone else to work on! For more information, please read the Contributing Guide.

Thank you so much for your contribution!

[bhargodevarya]

I would like to work on this.
So if the mutate is true, the last element from the array should be removed ? Does this mean that a new array of size n-1 with n-1 elements ??
Also, what should be the behavior if the array is empty or null ??