title: React-Native Firebase update column
body: <p>In Firebase database, I am trying to update one column only. 
  Firebase database 'users' JSON:</p>
  
  <pre><code> "users" : {
         "5yty2c8TyChQu3fMJ1O3d44wuq2" : {
         "Email" : "myEmail@yahoo.com",
         "FirstName" : "John",
         "LastName" : "Smith",
         "MobileNumber" : "",
         "NickName" : "",
         "profile_picture" : ""
    }
  </code></pre>
  
  <p>I would like to update just one column - MobileNumber with this code:</p>
  
  <pre><code>   updateMobileNumber(){
  
      var updateData = {
                      MobileNumber: this.state.mobileNumber
                        };
  
      var updates = {};
      updates['/users/' + userId ] = updateData;
  
      database.ref('users/' + userId).update(updates);
  
      alert('Account Updated');
  
     }
  </code></pre>
  
  <p>The above code instead of updating MobileNumber column, it is removing all the other columns and adding Email column. 
  What am I doing wrong ? I want to update Email column without touching other columns.
  Appreciate any help. </p>