Switch from request's window to traversable for user prompts (#724)

Follows whatwg/fetch#1823.

Author: domenic

index.bs

@@ -1934,8 +1934,8 @@ Content-Type: application/reports+json
                   :   <a for="request">origin</a>
                   ::  |violation|'s <a for="violation">global object</a>'s <a>relevant settings
                       object</a>'s <a for="environment settings object">origin</a>
-                  :   <a for="request">window</a>
-                  ::  "`no-window`"
+                  :   <a for="request">traversable for user prompts</a>
+                  ::  "`no-traversable`"
                   :   <a for="request">client</a>
                   ::  |violation|'s <a for="violation">global object</a>'s <a>relevant
                       settings object</a>