Use be_truthy and add back missing link

doc/ci/variables/README.md

@@ -399,6 +399,7 @@ export CI_REGISTRY_USER="gitlab-ci-token"
 export CI_REGISTRY_PASSWORD="longalfanumstring"
 ```
 
+[ce-13784]: https://gitlab.com/gitlab-org/gitlab-ce/issues/13784
 [runner]: https://docs.gitlab.com/runner/
 [triggered]: ../triggers/README.md
 [triggers]: ../triggers/README.md#pass-job-variables-to-a-trigger

spec/requests/api/variables_spec.rb

@@ -79,7 +79,7 @@ describe API::Variables do
         expect(response).to have_http_status(201)
         expect(json_response['key']).to eq('TEST_VARIABLE_2')
         expect(json_response['value']).to eq('VALUE_2')
-        expect(json_response['protected']).to eq(true)
+        expect(json_response['protected']).to be_truthy
       end
 
       it 'does not allow to duplicate variable key' do