Update rake requirement from ~> 13.0.0 to ~> 13.1.0 (#255)

Updates the requirements on [rake](https://github.com/ruby/rake) to permit the latest version.
- [Release notes](https://github.com/ruby/rake/releases)
- [Changelog](https://github.com/ruby/rake/blob/master/History.rdoc)
- [Commits](ruby/rake@v13.0.0...v13.1.0)

---
updated-dependencies:
- dependency-name: rake
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

pygments.rb.gemspec

@@ -24,7 +24,7 @@ Gem::Specification.new do |s|
 
   s.required_ruby_version = '>= 2.5.0'
 
-  s.add_development_dependency 'rake', '~> 13.0.0'
+  s.add_development_dependency 'rake', '~> 13.1.0'
   s.add_development_dependency 'rubocop', '~> 1.28.2'
   s.add_development_dependency 'test-unit', '~> 3.6.0'