Update slim_lint requirement from ~> 0.28.0 to ~> 0.31.0 (#567)

Updates the requirements on
[slim_lint](https://github.com/sds/slim-lint) to permit the latest
version.
<details>
<summary>Changelog</summary>
<p><em>Sourced from <a
href="https://github.com/sds/slim-lint/blob/main/CHANGELOG.md">slim_lint's
changelog</a>.</em></p>
<blockquote>
<h2>0.31.0</h2>
<ul>
<li>Add GitHub reporter</li>
</ul>
<h2>0.30.0</h2>
<ul>
<li>Speed up load time by preferring require_relative in internal gem
file loading</li>
</ul>
<h2>0.29.0</h2>
<ul>
<li>Add <code>TagAttribute</code> linter for restricting attribute
usage</li>
<li>Fix bug where <code>rexml</code> gem was missing if user used
RuboCop 1.66.0 or newer</li>
</ul>
<h2>0.28.0</h2>
<ul>
<li>Add <code>Tag</code> linter for restricting tag usage</li>
</ul>
<h2>0.27.0</h2>
<ul>
<li>Add <code>InstanceVariables</code> linter</li>
<li>Add <code>StrictLocalsMissing</code> linter</li>
<li>Fix <code>EmbeddedEngines</code> linter missing indented uses</li>
</ul>
<h2>0.26.0</h2>
<ul>
<li>Revert &quot;Fix <code>ControlSpacingStatement</code> linter
handling of <code>=</code> in some cases&quot;</li>
</ul>
<h2>0.25.0</h2>
<ul>
<li>Drop support for Ruby 2.x</li>
<li>Fix <code>ControlSpacingStatement</code> linter handling of
<code>=</code> in some cases</li>
</ul>
<h2>0.24.0</h2>
<ul>
<li>Require RuboCop 1.x or newer</li>
<li>Silence Parser gem warnings on startup</li>
</ul>
<h2>0.23.0</h2>
<ul>
<li>Add <code>Zwsp</code> to report zero-width space characters</li>
<li>Allow Slim version 5.x</li>
</ul>
<h2>0.22.1</h2>
<ul>
<li>Fix <code>CommentControlStatement</code> to not report
<code>Template Dependency:</code> directives</li>
<li>Fix handling of disabled lines when running across multiple
files</li>
<li>Add <code>Layout/ClosingParenthesisIndentation</code> to list of
ignored RuboCop cops</li>
<li>Add <code>Layout/FirstHashElementIndentation</code> to list of
ignored RuboCop cops</li>
</ul>
<h2>0.22.0</h2>
<!-- raw HTML omitted -->
</blockquote>
<p>... (truncated)</p>
</details>
<details>
<summary>Commits</summary>
<ul>
<li><a
href="https://github.com/sds/slim-lint/commit/695f0b18b5fc66b09ff5d368c37ffffc1a375f49"><code>695f0b1</code></a>
Cut version 0.31.0 (<a
href="https://redirect.github.com/sds/slim-lint/issues/189">#189</a>)</li>
<li><a
href="https://github.com/sds/slim-lint/commit/b4d1a5618d9000b5ba6bbd12f1de1d1d6adf0a84"><code>b4d1a56</code></a>
Create GitHub reporter (<a
href="https://redirect.github.com/sds/slim-lint/issues/188">#188</a>)</li>
<li><a
href="https://github.com/sds/slim-lint/commit/cf1f80b03bc2d6d7c619b8a76d9b8a1ff7b3dba8"><code>cf1f80b</code></a>
Remove note about Ruby 2.x support</li>
<li><a
href="https://github.com/sds/slim-lint/commit/0dd090377ec9254195b24ef50e560289cb92e826"><code>0dd0903</code></a>
Cut version 0.30.0 (<a
href="https://redirect.github.com/sds/slim-lint/issues/187">#187</a>)</li>
<li><a
href="https://github.com/sds/slim-lint/commit/6e4630d125d629ce8addff5e1155f8dc47955231"><code>6e4630d</code></a>
Prefer <code>require_relative</code> for internal requires (<a
href="https://redirect.github.com/sds/slim-lint/issues/186">#186</a>)</li>
<li><a
href="https://github.com/sds/slim-lint/commit/e8b26582f7a584384d78050caff9fdb2e0f4bac0"><code>e8b2658</code></a>
Cut version 0.29.0 (<a
href="https://redirect.github.com/sds/slim-lint/issues/185">#185</a>)</li>
<li><a
href="https://github.com/sds/slim-lint/commit/602bf48fb521755f0b98e5535ae67e29a5b89b6e"><code>602bf48</code></a>
Add TagAttribute linter (<a
href="https://redirect.github.com/sds/slim-lint/issues/183">#183</a>)</li>
<li><a
href="https://github.com/sds/slim-lint/commit/dc8b7d46c2c586d68baff2c842d0f0720275ea75"><code>dc8b7d4</code></a>
Add rexml as explicit dependency (<a
href="https://redirect.github.com/sds/slim-lint/issues/184">#184</a>)</li>
<li>See full diff in <a
href="https://github.com/sds/slim-lint/compare/v0.28.0...v0.31.0">compare
view</a></li>
</ul>
</details>
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</details>

govuk-components.gemspec

@@ -44,6 +44,6 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency("sass")
   spec.add_development_dependency("sassc", "~> 2.4.0")
   spec.add_development_dependency("slim", "~> 5.2.0")
-  spec.add_development_dependency("slim_lint", "~> 0.28.0")
+  spec.add_development_dependency("slim_lint", "~> 0.31.0")
   spec.add_development_dependency("webrick", "~> 1.8.1")
 end