Editorial: fix traverse history type (#601)

Author: jrandolf-2

index.bs

@@ -3495,10 +3495,10 @@ traverses the history of a given navigable by a delta.
    <dt>Command Type</dt>
    <dd>
       <pre class="cddl remote-cddl">
-      BrowsingContext.TraverseHistory = {
+      browsingContext.TraverseHistory = (
         method: "browsingContext.traverseHistory",
         params: browsingContext.TraverseHistoryParameters
-      }
+      )
 
       browsingContext.TraverseHistoryParameters = {
         context: browsingContext.BrowsingContext,