typo in comment

src/babylon.abstractScene.ts

@@ -138,7 +138,7 @@ module BABYLON {
 
         /**
         * All of the materials added to this scene
-        * In the context a the Scene, it is not supposed to be modified manually.
+        * In the context of a Scene, it is not supposed to be modified manually.
         * Any addition or removal should be done using the addMaterial and removeMAterial Scene methods.
         * Note also that the order of the Material wihin the array is not significant and might change.
         * @see http://doc.babylonjs.com/babylon101/materials
@@ -158,7 +158,7 @@ module BABYLON {
 
         /**
         * All of the tranform nodes added to this scene
-        * In the context a the Scene, it is not supposed to be modified manually.
+        * In the context of a Scene, it is not supposed to be modified manually.
         * Any addition or removal should be done using the addTransformNode and removeTransformNode Scene methods.
         * Note also that the order of the TransformNode wihin the array is not significant and might change.
         * @see http://doc.babylonjs.com/how_to/transformnode