Fix grammar

Author: frivoal

index.bs

@@ -1329,7 +1329,7 @@ Removing AB or TAG members</h5>
 	if the [=Advisory Committee Override=] proposal passes,
 	all seats on [=AB=] or [=TAG=] are [=vacated=] immediately;
 	if it fails, it cannot be invoked on the same body
-	sooner than six months since their previous invocation.
+	sooner than six months since its previous invocation.
 	The [=Team=] must announce the conclusion of the [=Advisory Committee Override=] to the [=Advisory Committee=].
 
 <h5 id="AB-TAG-vacated">