Update Face3.html

The face normal is wrong, which should points to the Z-direction.

docs/api/en/core/Face3.html

@@ -34,7 +34,7 @@ geometry.vertices.push( new THREE.Vector3(  50, -50, 0 ) );
 geometry.vertices.push( new THREE.Vector3(  50,  50, 0 ) );
 
 //create a new face using vertices 0, 1, 2
-var normal = new THREE.Vector3( 0, 1, 0 ); //optional
+var normal = new THREE.Vector3( 0, 0, 1 ); //optional
 var color = new THREE.Color( 0xffaa00 ); //optional
 var materialIndex = 0; //optional
 var face = new THREE.Face3( 0, 1, 2, normal, color, materialIndex );