Fix: Infinite hop calculation when there's a cycle
Fix: Infinite hop calculation when there's a cycle

There could be cases where `calculate` will hang because there is a
cycle in the `Map` of URLs.

e.g.:

  url1 --> url2
  url2 --> url1

`calculate` will now return if a `url` is already in the `hop` array.

This has happened a few times will debugging www.tmz.com.

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Close #486

alrra/sonar,sonarwhal/sonar,sonarwhal/sonar,alrra/sonar,alrra/sonar,sonarwhal/sonar