danger: help users to write server tests (#1970)

* danger: help users to write server tests

- fixes #1968
- adds the desired notice

* add trailing comma

https://circleci.com/gh/badges/shields/11866?utm_campaign=vcs-integration-link&utm_medium=referral&utm_source=github-build-link

dangerfile.js

@@ -65,7 +65,9 @@ if (packageJson.modified && !packageLock.modified) {
 if (server.modified && !serviceTests.createdOrModified) {
  warn([
  'This PR modified the server but none of the service tests. ',
- "That's okay so long as it's refactoring existing code.",
+ "That's okay so long as it's refactoring existing code. ",
+ "Otherwise, please consider adding tests to the service: ",
+ "https:/badges/shields/blob/master/doc/service-tests.md#readme",
  ].join(''));
 }