Replace approver

I mis-spelt "master" as "main" and caused this accidentally!

Author: dwd

xep-0066.xml

@@ -13,6 +13,7 @@
   <status>Draft</status>
   <type>Standards Track</type>
   <sig>Standards</sig>
+  <approver>Council</approver>
   <dependencies>
     <spec>XMPP Core</spec>
   </dependencies>