feat(pagespeedonline): update the API

#### pagespeedonline:v5
The following keys were added:
- schemas.PagespeedApiLoadingExperienceV5.properties.origin_fallback.description
- schemas.PagespeedApiLoadingExperienceV5.properties.origin_fallback.type

discovery/pagespeedonline-v5.json

@@ -174,7 +174,7 @@
       }
     }
   },
-  "revision": "20200318",
+  "revision": "20200608",
   "rootUrl": "https://pagespeedonline.googleapis.com/",
   "schemas": {
     "AuditRefs": {
@@ -503,6 +503,10 @@
           "description": "The map of <metrics, data>.",
           "type": "object"
         },
+        "origin_fallback": {
+          "description": "True if the result is an origin fallback from a page, false otherwise.",
+          "type": "boolean"
+        },
         "overall_category": {
           "description": "The human readable speed \"category\" of the id.",
           "type": "string"

src/apis/pagespeedonline/v5.ts

@@ -405,6 +405,10 @@ export namespace pagespeedonline_v5 {
      * The map of <metrics, data>.
      */
     metrics?: {[key: string]: Schema$UserPageLoadMetricV5} | null;
+    /**
+     * True if the result is an origin fallback from a page, false otherwise.
+     */
+    origin_fallback?: boolean | null;
     /**
      * The human readable speed "category" of the id.
      */