Fix typo

Co-authored-by: Yong <yy2452@columbia.edu>

ext-dynamic-commitments.md

@@ -369,7 +369,7 @@ secure in all contexts.
 Since the `initiator` is the one that is responsible for paying the fees for the
 kickoff transaction if it is required (like for certain `channel_type` changes),
 it follows that the `responder` cannot change the `channel_type`. Since the
-`kickoff_feerate` paid by the `initiator`, it should be set only if the sender
+`kickoff_feerate` is paid by the `initiator`, it should be set only if the sender
 is the `initiator`.
 
 The requirement for a node to remember what it last _sent_ and for it to