Freeze more development dependencies to get a green CI

Author: davidstosik

rspec_api_documentation.gemspec

@@ -33,6 +33,11 @@ Gem::Specification.new do |s|
   s.add_development_dependency "nokogiri", "~> 1.8.4"
   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 "gherkin", "~> 3.2.0"
+  s.add_development_dependency "multi_json", "~> 1.11.2"
+  s.add_development_dependency "rspec", "~> 3.4.0"
 
   s.files        = Dir.glob("lib/**/*") + Dir.glob("templates/**/*")
   s.require_path = "lib"