fix(util): add a test instead of throwing an error on getDocsUrl

[ranyitz]

getDocsUrl is a function that runs on the plugin's users machine, it returns a doc url, which is located on the remote.

The error should have verified that there is a corresponding doc file on the file system, which should indicate that the link won't be broken.

That logic can be done by a dedicated test, and by that, won't break the users in case this file does not exist.

note: In the test, we are using the rule key (name) from the main index.js, while the url is built from the __filename which should be the same as the key but i don't think that we verify that somewhere.