Update rspec requirement from ~> 3.9.0 to ~> 3.13.0 (#100)

Updates the requirements on [rspec](https://github.com/rspec/rspec-metagem) to permit the latest version.
- [Commits](rspec/rspec-metagem@v3.9.0...v3.13.0)

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

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

Gemfile

@@ -9,5 +9,5 @@ gem "activerecord", "~> #{ENV['ACTIVERECORD_VERSION']}" if ENV["ACTIVERECORD_VER
 group :test, :development do
   gem "gc_ruboconfig", "~> 5.0"
   gem "pg", "~> 1.4"
-  gem "rspec", "~> 3.9.0"
+  gem "rspec", "~> 3.13.0"
 end