prefer be_include over have_key in this case

sinatra-contrib/spec/cookies_spec.rb

@@ -559,7 +559,7 @@ def cookies(*set_cookies)
     it 'checks response cookies' do
       jar = cookies
       jar['foo'] = 'bar'
-      expect(jar).to have_key(:foo)
+      expect(jar).to be_include(:foo)
     end
 
     it 'does not use deleted cookies' do