Update MSC with MSC Number

proposals/4121-m.role.moderator.md

@@ -1,4 +1,4 @@
-# MSCXXXX: `m.role.moderator` `/.well-known/matrix/support` role.
+# MSC4121: `m.role.moderator` `/.well-known/matrix/support` role.
 
 ## Introduction
 
@@ -49,7 +49,7 @@ reports to the wrong bucket but that concern is already there with the current s
 
 ## Unstable prefix
 
-While this proposal is not yet accepted into the specification one should use `support.feline.mscXXXX.role.moderator`
+While this proposal is not yet accepted into the specification one should use `support.feline.msc4121.role.moderator`
 in place of `m.role.moderator`
 
 ## Dependencies