Fix tokenBinding definition type

Parent commit was generating the error:

    FATAL ERROR: Couldn't find target dict-member 'tokenBinding':
    <span data-dict-member-info="" for="CollectedClientData/tokenBinding"></span>

This is because the surrounding `<div dfn-type="dict-member"
dfn-for="CollectedClientData">` defines the definition type as `dict-member`,
but no such member is defined in the `CollectedClientData` dictionary.

This change overrides the definition type to `dfn`, which is described in the
Bikeshed docs [1] as "for general terms and phrases, and a catch-all for
anything else".

[1]: https://tabatkins.github.io/bikeshed/#dfn-types

index.bs

@@ -2988,7 +2988,7 @@ Note: The {{CollectedClientData}} may be extended in the future. Therefore it's
     ::  This OPTIONAL member contains the inverse of the `sameOriginWithAncestors` argument value
         that was passed into the [=internal method=].
 
-    :   \[RESERVED] <dfn>tokenBinding</dfn>        
+    :   \[RESERVED] <dfn dfn>tokenBinding</dfn>
     ::  This OPTIONAL member contains information about the state of the [=Token Binding=] protocol [[!TokenBinding]] used when communicating
         with the [=[RP]=]. Its absence indicates that the client doesn't support token binding