Fix RedBlackTree impl/test

[PatrykOlejniczak]

Hello,
after downloading the repository, I noticed that not all tests pass.
e.g. tests related with RedBlackTree.
I would like to work on these tests or implementation depends on what the problem will turn out to be if nobody else actual work with it?

I can also add some more unit test for that trees.

Regards.

[aalhour]

Hello @PatrykOlejniczak,

As I mentioned in the other issue, I'd be more than happy to review and accept contributions but after I get the unit tests fixed. If you can help me with that I'd appreciate it a lot! The problem is that Travis CI no longer runs the unit tests projects and I would like someone to help me fix that.

Cheers,
Ahmad