Update what's new.md

Updated demo

dist/preview release/what's new.md

@@ -30,7 +30,7 @@
     - New `Material.getBindedMeshes()` function ([deltakosh](https://github.com/deltakosh))
     - OimoJS Plugin now uses Quaternions exclusively and calculates body rotations correctly. [PR](https://github.com/BabylonJS/Babylon.js/pull/761) ([RaananW](https://github.com/RaananW))
     - It is now possible to get the physics engine's body and wolrd objects using the physics engine. [PR](https://github.com/BabylonJS/Babylon.js/pull/761) ([RaananW](https://github.com/RaananW))
-    - new Heightmap Impostor for Cannon.js physics engine. [PR](https://github.com/BabylonJS/Babylon.js/pull/78), [Demo] (http://www.babylonjs-playground.com/#EXL6K#1) ([RaananW](https://github.com/RaananW))
+    - new Heightmap Impostor for Cannon.js physics engine. [PR](https://github.com/BabylonJS/Babylon.js/pull/78), [Demo] (http://www.babylonjs-playground.com/#D3LQD#3) ([RaananW](https://github.com/RaananW))
     - A plane mesh can be created with a source plane (math). [PR](https://github.com/BabylonJS/Babylon.js/pull/779) ([RaananW](https://github.com/RaananW))
   - **Bug fixes**
     - Fixed a bug with spherical mapping ([deltakosh](https://github.com/deltakosh))