rename secrets.py to gb_secrets.py

A new Python 3.9 module "secrets" has been added, which breaks the
import command that is supposed to load the local file.

.gitignore

@@ -1,2 +1,2 @@
 __pycache__/
-secrets.py
+gb_secrets.py

app.py

@@ -1,5 +1,5 @@
 from flask import Flask, request
-from secrets import cookie
+from gb_secrets import cookie
 import requests
 import re