Add specific rubocop for tests

[VictorSNA]

We need to guarantee the code standard and quality in tests files!

For that mission we need to install, configure and fixes the offenses of rubocop-rspec:
https://github.com/rubocop/rubocop-rspec

Thanks!

DoD

• Rubocop-rspec installed and configured;
• No offenses being reported.

[eliseaston]

I will work on this issue

[VictorSNA]

Hi thanks for your interest, I'm assigning this issue to you!

[VictorSNA]

Hey I'm removing the assign, but feel free to claim it anytime!

Thanks!

[ifasanelli]

Hey @VictorSNA, can you assign me for this one, please?

[VictorSNA]

Hi @ifasanelli! I'm assigning you, thanks a lot!

[schmidt]

Started to work on this in #52. Kindly let me know how to proceed.