Update ruby_version requirement to allow Ruby 3.0

[johnny-1111one1]

rake spec passed with:

102 examples, 0 failures, 0 pending

[coveralls]

Pull Request Test Coverage Report for Build 260

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 99.257%

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Totals
Change from base Build 250:	0.0%
Covered Lines:	668
Relevant Lines:	673

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💛 - Coveralls

[rarruda]

Hi,

Thanks for the contribution!

I pulled your branch/commit into a local branch (see PR #44), before merging to master in a separate PR (#45).

I see that one gem needs to be updated for ruby 3.0.0 to work as expected, the travis build config and the README also needs to be updated. I will follow up these changes in PR #45.

Closing this PR, but your commit should be getting merged soon.