Replace rest-client with http.rb

[oskaror]

Fix #21
Currently, we use the rest-client gem, but it's a very heavy-weight library, so I replaced it with http.rb

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Before submitting the PR make sure the following are checked:

• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Ran bundle exec rake default. It executes all tests and runs RuboCop on its own code.

[Neodelf]

I am checking what's going on

[Neodelf]

@oskaror I didn't greet you. I am so sorry. I really tried to fast solve the problem 💨
Thank you for your updates! I really appreciate it! ❤️
So I set the simplecov gem version directly. Please, rebase the branch from master. Hope it helps.
Also, please update CHANGELOG.md

[Neodelf]

Thank you for your work!

[Neodelf]

@all-contributors please add @oskaror for code

[allcontributors]

@Neodelf

I've put up a pull request to add @oskaror! 🎉