message: Add translation strings for "Exposed Metrics" challenge
diff: " <em>(This challenge is <strong>not available</strong> on Docker!)</em>": " <em>(This challenge is <strong>not available</strong> on Docker!)</em>",
  " <em>(This challenge is <strong>not available</strong> on Heroku!)</em>": " <em>(This challenge is <strong>not available</strong> on Heroku!)</em>",
  " <em>(This challenge is <strong>potentially harmful</strong> on Docker!)</em>": " <em>(This challenge is <strong>potentially harmful</strong> on Docker!)</em>",
  - " <em>(This challenge is <strong>potentially harmful</strong> on Heroku!)</em>": " <em>(This challenge is <strong>potentially harmful</strong> on Heroku!)</em>"
  + " <em>(This challenge is <strong>potentially harmful</strong> on Heroku!)</em>": " <em>(This challenge is <strong>potentially harmful</strong> on Heroku!)</em>",
  + "Find the endpoint that serves usage data to be scraped by a <a href=\"https://github.com/prometheus/prometheus\">popular monitoring system</a>.": "Find the endpoint that serves usage data to be scraped by a <a href=\"https://github.com/prometheus/prometheus\">popular monitoring system</a>.",
  + "Try to guess what URL the endpoint might have.": "Try to guess what URL the endpoint might have."
  }
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