Typo.

src/Lights/babylon.directionalLight.ts

@@ -63,7 +63,7 @@
         /**
          * Creates a DirectionalLight object in the scene, oriented towards the passed direction (Vector3).  
          * The directional light is emitted from everywhere in the given direction.  
-         * It can cast shawdows.
+         * It can cast shadows.
          * Documentation : http://doc.babylonjs.com/tutorials/lights
          * @param name The friendly name of the light
          * @param direction The direction of the light
@@ -230,4 +230,4 @@
             defines["DIRLIGHT" + lightIndex] = true;
         }
     }
-}  
+}