Notice of Filing and Immediate Effectiveness of a Proposed Rule Change To Amend the Description of Price Improving Orders Under Subparagraph (6) to Rule 21.1(d) and Add Subparagraph (4) to Rule 21.1(h) Modifying the Operation of Orders Subject to the Display Price Sliding Process When a Contra-Side Post Only Order Is Received by the Bats EDGX Exchange Options Platform