Update Article.js

models/Article.js

@@ -12,7 +12,7 @@ var ArticleSchema = new mongoose.Schema({
   comments: [{ type: mongoose.Schema.Types.ObjectId, ref: 'Comment' }],
   tagList: [{ type: String }],
   author: { type: mongoose.Schema.Types.ObjectId, ref: 'User' }
-}, {timestamps: true, usepPushEach: true});
+}, {timestamps: true, usePushEach: true});
 
 ArticleSchema.plugin(uniqueValidator, {message: 'is already taken'});