Update part12b.md

Author: d-stn

src/content/12/en/part12b.md

@@ -392,7 +392,7 @@ MongoError: command find requires authentication
 
 ### Bind mount and initializing the database
 
-In the [MongoDB Docker Hub](https://hub.docker.com/_/mongo) page under "Initializing a fresh instance" is the info on how to execute JavaScript to initialize the database and an user for it.
+In the [MongoDB Docker Hub](https://hub.docker.com/_/mongo) page under "Initializing a fresh instance" is the info on how to execute JavaScript to initialize the database and a user for it.
 
 The exercise project has a file <i>todo-app/todo-backend/mongo/mongo-init.js</i> with contents: