docs: Fix Docker Hub documentation logo
docs: Fix Docker Hub documentation logo

The URL got broken when www.scylladb.com changed. Fix it up.

Message-Id: <90fc32a5c69c425601dec524325ebfe9d1a41791@scylladb.com>

avikivity/scylla,avikivity/scylla,duarten/scylla,duarten/scylla,scylladb/scylla,scylladb/scylla,avikivity/scylla,scylladb/scylla,scylladb/scylla,duarten/scylla