Update rake requirement from ~> 13.1.0 to ~> 13.2.1 (#539)

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@v13.1.0...v13.2.1)

---
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>

statesman.gemspec

@@ -28,7 +28,7 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency "mysql2", ">= 0.4", "< 0.6"
   spec.add_development_dependency "pg", ">= 0.18", "<= 1.6"
   spec.add_development_dependency "rails", ">= 5.2"
-  spec.add_development_dependency "rake", "~> 13.1.0"
+  spec.add_development_dependency "rake", "~> 13.2.1"
   spec.add_development_dependency "rspec", "~> 3.1"
   spec.add_development_dependency "rspec-github", "~> 2.4.0"
   spec.add_development_dependency "rspec-its", "~> 1.1"