Fix the grammar for CallbackInterfaceMembers. (#753)

I accidentally missed a letter in #705.

Fixes #751.

Author: Ms2ger

index.bs

@@ -1445,7 +1445,7 @@ must be annotated with an [{{Exposed}}] [=extended attribute=].
 
 <pre class="grammar" id="prod-CallbackInterfaceMembers">
     CallbackInterfaceMembers :
-        ExtendedAttributeList CallbackInterfaceMember CallbackInterfaceMember
+        ExtendedAttributeList CallbackInterfaceMember CallbackInterfaceMembers
         ε
 </pre>
 
@@ -13624,6 +13624,7 @@ Jens Lindström,
 Peter Linss,
 呂康豪 (Kang-Hao Lu),
 Kyle Machulis,
+Darien Maillet Valentine,
 Mark Miller,
 Ms2ger,
 Andrew Oakley,