Update rspec requirement from ~> 3.12.0 to ~> 3.13.0 (#48)

Updates the requirements on [rspec](https://github.com/rspec/rspec-metagem) to permit the latest version.
- [Commits](rspec/rspec-metagem@v3.12.0...v3.13.0)

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

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

dyck.gemspec

@@ -19,7 +19,7 @@ Gem::Specification.new do |s|
   s.require_paths = ['lib']
 
   s.add_development_dependency 'rake', '~> 13.1.0'
-  s.add_development_dependency 'rspec', '~> 3.12.0'
+  s.add_development_dependency 'rspec', '~> 3.13.0'
   s.add_development_dependency 'rubocop', '~> 1.28.2'
   s.add_development_dependency 'rubocop-rake', '~> 0.6.0'
   s.add_development_dependency 'rubocop-rspec', '~> 2.10.0'