Fix offenses newly reported by rubocop-rspec

[avdv]

Description

The pessimistic version contraint on rubocop-rspec permitted minor version
updates of the dependency, which broke the tests again since version 2.9.0
introduced / changed offenses:

rbbe rake rubocop:auto_correct
Running RuboCop...
Inspecting 22 files
.................CC...

Offenses:

spec/color_ls/yaml_spec.rb:20:47: C: [Corrected] RSpec/BeEq: Prefer be over eq.
        expect(checker.sorted?(sort_type)).to eq true
                                              ^^
spec/color_ls_spec.rb:7:37: C: [Corrected] RSpec/BeNil: Prefer be_nil over be(nil).
    expect(ColorLS::VERSION).not_to be nil
                                    ^^^^^^

22 files inspected, 2 offenses detected, 2 offenses corrected

Allow only the patch version to increase automatically to avoid this in the future.

• Relevant Issues : (none)
• Relevant PRs : (none)
• Type of change :
  • New feature
  • Bug fix for existing feature
  • Code quality improvement
  • Addition or Improvement of tests
  • Addition or Improvement of documentation