Fix typo.

models/cards.js

@@ -1022,7 +1022,7 @@ if (Meteor.isServer) {
     // When loading a board, mongodb is searching for every cards, the id of the parent (in the swinglanes collection).
     // With a huge database, this result in a very slow app and high CPU on the mongodb side.
     // To correct it, add Index to parentId:
-    Cards._collection._ensureIndex({"parentId": 1});
+    Cards._collection._ensureIndex({parentId: 1});
   });
 
   Cards.after.insert((userId, doc) => {