Update IETF-RFC.md

Co-authored-by: Giuseppe Lo Presti <giuseppe.lopresti@cern.ch>

Author: mickenordin

IETF-RFC.md

@@ -1444,7 +1444,7 @@ format:
 
 An implementor of OCM MAY choose any internal object model to represent
 an _Address Book_, a _Contact_, an _Invite_, a _Provider_, a _Share_,
-and  a _User_.  However, the following diagrams are provided to clarify
+and a _User_.  The following diagrams are provided to clarify
 the concepts and their relationships, as a guide for implementors.
 
 ## Address Book