Include a timestamp in the result json (#4147)

Author: soulgalore

lib/sitespeed.js

@@ -177,7 +177,8 @@ export async function run(options) {
         ? resultUrls.reportSummaryUrl() + '/index.html'
         : '',
       pageSummaryUrl,
-      localPath: storageManager.getBaseDir()
+      localPath: storageManager.getBaseDir(),
+      timestamp: timestamp.format()
     };
   } catch (error) {
     log.error(error);