Fix spelling errors (knative#1990)

Produced via:
  `github.com/client9/misspell`
/assign samodell

docs/serving/samples/cloudevents/cloudevents-go/cloudevents.go

@@ -29,7 +29,7 @@ func main() {
 		log.Fatal(err.Error())
 	}
 
-	// Depending on whether targetting data has been supplied,
+	// Depending on whether targeting data has been supplied,
 	// we will either reply with our response or send it on to
 	// an event sink.
 	var receiver interface{} // the SDK reflects on the signature.