Bump rainbow from 3.0.0 to 3.1.1

[dependabot[bot]]

Bumps rainbow from 3.0.0 to 3.1.1.

Changelog

Sourced from rainbow's changelog.

3.1.1 (2021-01-11)

• fix: Ensure files directive in gemspec adds all files

3.1.0 (2021-01-11)

• Bad release: superseded by 3.1.1.
• added cross_out aka strike
• hexadecimal color names supported better, see #83
• gemspec: list files using a Ruby expression, avoiding git

(2020-08-26 was the planned release date, but the real release date is reflected in the heading.)

Commits

• d5e2071 v3.1.1
• d96abce fix: Include all lib/ files
• ea58198 Add screenshot of example in README
• ed22e0a Update .travis.yml
• 3fa4817 Update .travis.yml
• 0c0eb63 RuboCop: configure new 0.81.0 rules
• 88f4110 Pin RuboCop to 0.81.0 to support Ruby 2.3
• 8a2e318 v3.1.0
• 7f65e69 v3.1.0 Changelog
• ae68805 (chore) Add v0.80 RuboCop cops
• Additional commits viewable in compare view

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This change is 

[david942j]

@dependabot rebase

[dependabot[bot]]

Looks like this PR is already up-to-date with master! If you'd still like to recreate it from scratch, overwriting any edits, you can request @dependabot recreate.

[david942j]

@dependabot recreate

[dependabot[bot]]

Looks like rainbow is no longer updatable, so this is no longer needed.