title: Mongoose query problem - $push pushing element twice
body: <p>I want to push single string into array from document in my mongodb collection.
  I'm using nodejs with mongoose v5.3.1</p>
  
  <p>I'm putting data into my html form and then, submitting it to server.</p>
  
  <p>There is my HTML:</p>
  
  <pre><code>&lt;form action="/addchat" method="post"&gt;
              &lt;input type="text" class="form-control" name="chatid" id="addchatid"&gt;
              &lt;input type="text" class="form-control" name="chatname"&gt;
              &lt;select class="form-control form-control-sm" name="chatbot" id="chatbot"&gt;
              &lt;option value="684206793:AAH5uDpus4Ngw1Z60pj6iOedBGCM8Vq0"&gt;botname1&lt;/option&gt;&lt;/select&gt;&lt;br&gt;
              &lt;button type="submit" class="btn btn-primary"&gt;Add&lt;/button&gt;
  &lt;/form&gt;
  </code></pre>
  
  <p>There is my app code:</p>
  
  <pre><code>app.post('/addchat', async (req, res) =&gt; {
  
      var czat = {
        name: req.body.chatname,
        chatid: req.body.chatid
      }
  
      await botsmodel.updateOne({
          token: req.body.chatbot
        }, {
          $push: {
            chats: czat
          }
        },
        async (err, result) =&gt; {
          if (err) {
            console.log(`Error updating chats ${err}`)
          } else {
            console.log(`Chats updated for ${req.body.chatbot}`);
          }
  
        });
  
  
      await res.redirect('/')
  
  
  });
  </code></pre>
  
  <p>There is my collection schema:</p>
  
  <pre><code>var schemaOptions = {
    timestamps: true,
    toJSON: {
      virtuals: true
    },
    toObject: {
      virtuals: true
    }
  };
  
  var botyschema = new mongoose.Schema({
    _id: String,
    name: String,
    token: String,
    chats: Array
  }, schemaOptions);
  </code></pre>
  
  <p>After executing, my console looks like it have pushed "czat" object once:</p>
  
  <pre><code>Chats updated for 684206793:AAH5uDpus4Ngw1Z60pj6iOedBGCM8Vq0
  </code></pre>
  
  <p>But in my collection two objects have appended into my array, it looks that:</p>
  
  <pre><code> "chats": [
              {
                  "name": "chat_main",
                  "chatid": "100516120633"
              },
              {
                  "name": "chat_main",
                  "chatid": "100516120633"
              }
            ],
  </code></pre>
  
  <p>I'm missing something in my schema or query?</p>