Update what's new

dist/preview release/what's new.md

@@ -18,6 +18,7 @@
 - Added support for Particle animation in ParticleSystem. [Doc here](http://doc.babylonjs.com/tutorials/particles#particle-animation) ([Ibraheem Osama](https://github.com/IbraheemOsama))
 
 ## Updates
+- Added `MultiObserver`. [Doc here](http://doc.babylonjs.com/overviews/observables#multiobserver) ([deltakosh](https://github.com/deltakosh))
 - Added `shadowGenerator.addShadowCaster` and `shadowGenerator.removeShadowCaster` helper functions ([deltakosh](https://github.com/deltakosh))
 - Several inspector improvements ([temechon](https://github.com/temechon))
 - New observables for actions: `onBeforeExecuteObservable` for all actions and `onInterpolationDoneObservable` for `InterpolateValueAction` ([deltakosh](https://github.com/deltakosh))