title: How to update an attribute in loopback by updateOrCreate?
body: <p>I want to update an attribute by remote method but it is not working correctly,
  I want to post age to from app to backend and update it in the backend.</p>
  
  <pre><code>Person.testupdate = function ( id, age, cb) {
      Person.upsertWithWhere({
        where: {
          id: id
        },
  
          age: age,
      },
        function (err, Person) {
          cb(null, Person);
        });
    }
  
    Person.remoteMethod('testupdate', {
      accepts: [{
        arg: 'id',
        type: 'string'
      }
  ],
      returns: {
        arg: 'result',
        type: 'string'
      },
      http: {
        path: '/updateage',
        verb: 'get'
      }
    });
  
  };
  </code></pre>