Update contracts requirement from ~> 0.13.0 to ~> 0.17

Updates the requirements on [contracts](https://github.com/egonSchiele/contracts.ruby) to permit the latest version.
- [Changelog](https://github.com/egonSchiele/contracts.ruby/blob/master/CHANGELOG.markdown)
- [Commits](egonSchiele/contracts.ruby@v0.13.0...v0.17)

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

Signed-off-by: dependabot[bot] <[email protected]>

rspec_api_documentation.gemspec

@@ -33,7 +33,7 @@ Gem::Specification.new do |s|
   s.add_development_dependency "yard", "~> 0.9.15"
   s.add_development_dependency "inch", "~> 0.8.0"
   s.add_development_dependency "minitest", "~> 5.8.4"
-  s.add_development_dependency "contracts", "~> 0.13.0"
+  s.add_development_dependency "contracts", "~> 0.17"
   s.add_development_dependency "gherkin", "~> 3.2.0"
   s.add_development_dependency "multi_json", "~> 1.11.2"
   s.add_development_dependency "rspec", "~> 3.4.0"