title: Mongoose change populated field name after populate
body: <p>In mongoose, I am using populate on field. After populate need to change field name. Is it possible?</p>
  
  <p>I am populate on company_id. It is showing me company_id: Object but I need to change its name as company:Object.</p>
  
  <pre><code>    this.model(companySessionModelName)
      .find(
            {
              "company_session.end_date":{$lt:arg_date},
              "company_session.status":"active"
            },
            {
              "company_id":1,
              "company_session.$":1
            }
          )
  .populate("company_id","name")                                            
  .exec(function(err, _s_user) {
           if(err){
             cb(err);
           }else{
              cb(null,_s_user);
           }   });
  </code></pre>
  
  <blockquote>
    <p>Output:</p>
  </blockquote>
  
  <pre><code>[
              {
                  "_id": "5a829132a83f321e380cd17f",
                  "company_id": {
                      "_id": "5a7ad080f8c88a231113676f",
                      "name": "Stephania Rath"
                  },
                  "company_session": [
                      {
                          "start_date": "2018-02-14T00:00:00.000Z",
                          "end_date": "2018-02-16T00:00:00.000Z",
                          "_id": "5a829132a83f321e380cd180",
                          "status": "active"
                      }
                  ]
              }
          ]
  </code></pre>
  
  <blockquote>
    <p>Excepted Output:</p>
  </blockquote>
  
  <pre><code>[
              {
                  "_id": "5a829132a83f321e380cd17f",
                  "company": {
                      "_id": "5a7ad080f8c88a231113676f",
                      "name": "Stephania Rath"
                  },
                  "company_session": [
                      {
                          "start_date": "2018-02-14T00:00:00.000Z",
                          "end_date": "2018-02-16T00:00:00.000Z",
                          "_id": "5a829132a83f321e380cd180",
                          "status": "active"
                      }
                  ]
              }
          ]
  </code></pre>