Update rspec

This fixes usage with Ruby 3.3

schleuder-cli.gemspec

@@ -24,5 +24,5 @@ Gem::Specification.new do |s|
   if Gem::Version.new(RUBY_VERSION) >= Gem::Version.new("3.3.0")
     s.add_runtime_dependency 'base64', '~> 0.2.0'
   end
-  s.add_development_dependency 'rspec', '~> 3.5.0'
+  s.add_development_dependency 'rspec', '~> 3.13'
 end