Docs: Investigate why scaladoc links for pekko-http and pekko-grpc are broken

[pjfanning]

Found in #919.

    # Invalid links generated in Google Common Connector scaladoc
    "https://pekko.apache.org/api/pekko-http/"
    # Invalid links generated in Google Pubsub Connector scaladoc
    "https://pekko.apache.org/api/pekko-grpc/"

The broken links are in #919 (comment)