Update mongo.md

Author: kamilmysliwiec

content/techniques/mongo.md

@@ -77,14 +77,14 @@ In case you want to specify relation to another model, later for populating, you
 import * as mongoose from 'mongoose';
 import { Owner } from '../owners/schemas/owner.schema';
 
-@Prop({ type: mongoose.Schema.Types.ObjectId, ref: Owner.name })
+@Prop({ type: mongoose.Schema.Types.ObjectId, ref: 'Owner' })
 owner: Owner;
 ```
 
 In case there are multiple owners, your property configuration should look as follows:
 
 ```typescript
-@Prop({ type: [{ type: mongoose.Schema.Types.ObjectId, ref: Owner.name }] })
+@Prop({ type: [{ type: mongoose.Schema.Types.ObjectId, ref: 'Owner' }] })
 owner: Owner[];
 ```