Save start and end revisions in cache

.github/change_log.py

@@ -405,11 +405,15 @@ def parse_arguments():
     pr_info = fetch_pr_info(prs, auth=args.auth)
     if args.cache:
         with open(args.cache, "w") as fp:
-            fp.write(json.dumps(pr_info))
+            d = {'start': args.start, 'end': args.end, 'pr_info': pr_info}
+            fp.write(json.dumps(d))
 else:
     # Load previously cached info
     with open(args.from_cache) as fp:
-        pr_info = json.loads(fp.read())
+        d = json.loads(fp.read())
+        pr_info = d['pr_info']
+        args.start = d['start']
+        args.end = d['start']
 
 
 # Generate text content based on changes