title: ng2 select2 [data]. Not working if 'id' is different of 'text'
body: <p>I have a issue with ng2 select2 plugin for angular 4. Indeed, if my id is different of my text, the plugin bug and nothing is showing in the select2 after clicking on the dropdown value (value is "null")... </p>
  
  <p>I just reproduce this component, (<a href="https://github.com/NejcZdovc/ng2-select2-demo/tree/master/src/app/demos/basic" rel="nofollow noreferrer">https://github.com/NejcZdovc/ng2-select2-demo/tree/master/src/app/demos/basic</a>) and I have the same problem... On init the value is showing well. But when I change the value of the input, the select doesn't show anythings... 
  See bellow the few steps to understand what I mean.</p>
  
  <p><a href="https://i.stack.imgur.com/uD75Y.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/uD75Y.png" alt="enter image description here"></a></p>
  
  <p><a href="https://i.stack.imgur.com/1GEpW.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/1GEpW.png" alt="enter image description here"></a></p>
  
  <p><a href="https://i.stack.imgur.com/9XPZc.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/9XPZc.png" alt="enter image description here"></a></p>
  
  <p><a href="https://i.stack.imgur.com/aibKb.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/aibKb.png" alt="enter image description here"></a></p>
  
  <p><a href="https://i.stack.imgur.com/nYDII.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/nYDII.png" alt="enter image description here"></a></p>
  
  <p>Does someone have a solution to solve this bug ? Thank you</p>