Fixed webvr_rollercoaster orientation.

examples/webvr_rollercoaster.html

@@ -229,7 +229,7 @@
 				velocity -= tangent.y * 0.0000015;
 				velocity = Math.max( velocity, 0.00004 );
 
-				train.lookAt( lookAt.copy( position ).add( tangent ) );
+				train.lookAt( lookAt.copy( position ).sub( tangent ) );
 
 				//