Remove redundant "in parallel"

Author: yoshisatoyanagisawa

docs/index.bs

@@ -1618,10 +1618,9 @@ spec: storage; urlPrefix: https://storage.spec.whatwg.org/
             Note: {{InstallEvent/addRoutes(rules)|event.addRoutes(rules)}} extends the lifetime of the event by default as if {{ExtendableEvent/waitUntil()|event.waitUntil(promise)}} is called.
 
         1. Let |promise| be a new [=promise=].
-        1. [=In parallel=]:
-            1. Upon [=upon fulfillment|fulfillment=] or [=upon rejection|rejection=] of |promise|, resolve |lifetimePromise| with undefined.
+        1. Upon [=upon fulfillment|fulfillment=] or [=upon rejection|rejection=] of |promise|, resolve |lifetimePromise| with undefined.
 
-                Note: this step is for making |lifetimePromise| always fullfilled to avoid the install event failure.
+            Note: this step is for making |lifetimePromise| always fullfilled to avoid the install event failure.
 
         1. Let |serviceWorkerEventLoop| be the [=current global object=]'s [=event loop=].
         1. [=Queue a task=] to run the following steps on |serviceWorkerEventLoop| using the [=DOM manipulation task source=]: