fix REDIS_USERNAME format (#414)

api/.env.example

@@ -22,7 +22,7 @@ CELERY_BROKER_URL=redis://:difyai123456@localhost:6379/1
 # redis configuration
 REDIS_HOST=localhost
 REDIS_PORT=6379
-REDIS_USERNAME: ''
+REDIS_USERNAME=
 REDIS_PASSWORD=difyai123456
 REDIS_DB=0
 
@@ -90,4 +90,4 @@ SQLALCHEMY_ECHO=false
 NOTION_INTEGRATION_TYPE=public
 NOTION_CLIENT_SECRET=you-client-secret
 NOTION_CLIENT_ID=you-client-id
-NOTION_INTERNAL_SECRET=you-internal-secret
+NOTION_INTERNAL_SECRET=you-internal-secret