Update environment.md fix environment mongo username (#1847)

Author: cubxxw

docs/contrib/environment.md

@@ -311,7 +311,7 @@ This section involves setting up MongoDB, including its port, address, and crede
 | MONGO_ADDRESS  | [Generated IP] | IP address for MongoDB. |
 | MONGO_USERNAME | [User Defined] | Admin Username for MongoDB.   |
 | MONGO_PASSWORD | [User Defined] | Admin Password for MongoDB.   |
-| MONGO_OPENIM_PASSWORD | [User Defined] | OpenIM Username for MongoDB.   |
+| MONGO_OPENIM_USERNAME | [User Defined] | OpenIM Username for MongoDB.   |
 | MONGO_OPENIM_PASSWORD | [User Defined] | OpenIM Password for MongoDB.   |
 
 ###  2.8. <a name='TencentCloudCOSConfiguration'></a>Tencent Cloud COS Configuration