Update rake requirement from ~> 13.0.0 to ~> 13.1.0

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] <support@github.com>

asciidoctor-epub3.gemspec

@@ -34,7 +34,7 @@ An extension for Asciidoctor that converts AsciiDoc documents to EPUB3 and KF8/M
   s.add_development_dependency 'asciimath', '~> 2.0'
   s.add_development_dependency 'coderay', '~> 1.1.0'
   s.add_development_dependency 'pygments.rb', '~> 2.4.0'
-  s.add_development_dependency 'rake', '~> 13.0.0'
+  s.add_development_dependency 'rake', '~> 13.1.0'
   s.add_development_dependency 'rouge', '~> 3.0'
   s.add_development_dependency 'rspec', '~> 3.12.0'
   s.add_development_dependency 'rubocop', '~> 1.28.2'