fix port

mantisbt/README.md

@@ -1,5 +1,7 @@
 MantisBT is an open source issue tracker that provides a delicate balance between simplicity and power.
 
+WARNING: This is still a work in progress, a successful connection has not been made.
+
 
 ## docker-compose.yml
 
@@ -15,8 +17,7 @@ mantisbt:
 db:
   image: mariadb
   environment:
-    - MYSQL_USERNAME=root
-    - MYSQL_PASSWORD=root
+    - MYSQL_ROOT_PASSWORD=root
     - MYSQL_DATABASE=bugtracker
   restart: always
 ```