set empty config defaults on make_app()

autovpn/vpn_app.py

@@ -182,7 +182,7 @@ def new_cert_dl():
     return response
 
 
-def make_app(config):
+def make_app(config={}):
     app = Flask(__name__)
     app.config.update(config)
     app.config.from_envvar('VPN_APP_SETTINGS', silent=True)