Fixed bad gremlin.sh link for 3.1.8 release.
Fixed bad gremlin.sh link for 3.1.8 release.

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