Update docs/index.bs

- remvoed unnecessary type check.  I added that for allowing the argument
  to be Promsie, which I reverted.
- move fetch-event check inside the loop to make the code a bit simpler.

Author: yoshisatoyanagisawa

docs/index.bs

@@ -1607,12 +1607,11 @@ spec: storage; urlPrefix: https://storage.spec.whatwg.org/
 
         1. Let |event| be [=this=].
         1. If |event|'s [=dispatch flag=] is unset, [=throw=] an "{{InvalidStateError}}" {{DOMException}}.
-        1. If |rules| is not either of a {{RouterRule}} dictionary or a sequence of {{RouterRule}} dictionaries, then return [=a promise rejected with=] a {{TypeError}}.
         1. If |rules| is a {{RouterRule}} dictionary, set |rules| to « |rules| ».
         1. Let |serviceWorker| be the [=current global object=]'s associated [=ServiceWorkerGlobalScope/service worker=].
         1.  For each |rule| of |rules|:
             1. If running the [=Verify Router Condition=] algorithm with |rule|["{{RouterRule/condition}}"] and |serviceWorker| returns false, return [=a promise rejected with=] a {{TypeError}}.
-        1. If |rules| [=list/contains=] a {{RouterRule}} whose {{RouterRule/source}} is "{{RouterSourceEnum/fetch-event}}" and |serviceWorker|'s [=set of event types to handle=] does not [=set/contain=] {{ServiceWorkerGlobalScope/fetch!!event}}, return [=a promise rejected with=] a {{TypeError}}.
+            1. If |rule|["{{RouterRule/source}}"] is "{{RouterSourceEnum/fetch-event}}" and |serviceWorker|'s [=set of event types to handle=] does not [=set/contain=] {{ServiceWorkerGlobalScope/fetch!!event}}, return [=a promise rejected with=] a {{TypeError}}.
         1. Let |promise| be a new [=promise=].
         1. [=ExtendableEvent/Add lifetime promise=] |promise| to |event|.