Update slim requirement from ~> 4.1 to ~> 5.1

[dependabot]

Updates the requirements on slim to permit the latest version.

Changelog

Sourced from slim's changelog.

5.1.0 (2023-03-06)

• Allow whitespace markers for verbatim text: |<, |>, and |<> - #912
• Do not swallow single quote after output line indicator - #911
• Support Tilt 2.1.0 - #910
• Fix Railtie load error - #904
• Fix attribute parsing with square brackets - #796

5.0.0 (2023-01-23)

• Fix markdown interpolation #773
• Support case/in #884
• Extract slim/railtie #850
• css: doesn't add type='text/css' anymore #828
• Remove deprecated whitespace syntax =' etc
• Add support for annotate_rendered_view_with_filenames #867, #878, #901
• Remove deprecated syntax
• Add option to hyphenate underscore attributes - #852
• Update CI/CD testing and dependencies

4.1.0 (2020-05-07)

• Add support for Tailwind CSS - #841
• Update dependencies and testing

4.0.1 (2018-09-02)

• Fix incompatibility issue with Slim Include plugin and new ability to specifiy attributes for embedded engines #819

4.0.0 (2018-08-26)

• Add ability to specify attributes for embedded engines using TagEngine - #653
• Set Tilt's default encoding to utf-8 - #800
• Prevent generation of invalid Ruby code in heredoc - #770
• Don't convert underscores to dashes on data attributes - #807 [Backward incompatible]
• Update description in README.jp.md - #795
• Removed support for embedded engines: Asciidoc, Builder, Creole, Erb, Nokogiri, Opal, Org-Ruby, Styl, Wikicloth
• Fix tests

3.0.9 (2017-11-09)

• Fixed Cross-site Scripting in splat attributes names (See #767)
• Restrict access to public methods in logic_less templates (See #781)

3.0.8 (2017-05-06)

• Added splat_prefix configuration option for Angular2 syntax support
• Require Ruby >= 2.0.0
• Relax temple dependency

3.0.7 (2016-05-22)

... (truncated)

Commits

• f453280 Version 5.1.0
• bdfc1ac Update changelog
• e924243 Allow whitespace markers for verbatim text: |\<, |>, and |\<> (#912)
• 3b10346 Remove broken badges (Fix #908)
• ea64a92 Do not swallow single quote after output line indicator (#911)
• 8a9af5d Allow Slim to be used with Tilt 2.1.0 (#910)
• 29d2647 Remove benchmarks (Moved to https://github.com/slim-template/benchmarks)
• e741223 Fix Railtie load error (#904)
• 7d90b98 Update gemfile
• a8f84ca Update gemfile
• Additional commits viewable in compare view

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