Minor change to wording on listing policy.
Minor change to wording on listing policy.

Listing policy applies to any gremlin tools, not just "middleware", given the addition of the "powered by" section. https://lists.apache.org/thread.html/ae366b601fdbdfd7d49cb62b5c6a57bc74f29d6ab8d70d8df3e4e75f@%3Cdev.tinkerpop.apache.org%3E CTR

artem-aliev/tinkerpop,jorgebay/tinkerpop,apache/tinkerpop,artem-aliev/tinkerpop,robertdale/tinkerpop,apache/tinkerpop,krlohnes/tinkerpop,robertdale/tinkerpop,robertdale/tinkerpop,jorgebay/tinkerpop,krlohnes/tinkerpop,artem-aliev/tinkerpop,robertdale/tinkerpop,krlohnes/tinkerpop,apache/incubator-tinkerpop,jorgebay/tinkerpop,apache/incubator-tinkerpop,apache/incubator-tinkerpop,krlohnes/tinkerpop,jorgebay/tinkerpop,artem-aliev/tinkerpop,apache/tinkerpop,robertdale/tinkerpop,apache/tinkerpop,krlohnes/tinkerpop,pluradj/incubator-tinkerpop,apache/tinkerpop,apache/tinkerpop,artem-aliev/tinkerpop,pluradj/incubator-tinkerpop,pluradj/incubator-tinkerpop,apache/tinkerpop