fix Filename to RelativeFilename in parseImage()

The path of "Filename" property is useless. It depends on local directory (ex. C:\somewhere\blahblah\shitty.fbx). RelativeFilename is better for URI.

examples/js/loaders/FBXLoader.js

@@ -173,7 +173,7 @@
 
 				var id = parseInt( nodeID );
 
-				images[ id ] = videoNode.Filename;
+				images[ id ] = videoNode.RelativeFilename || videoNode.Filename;
 
 				// raw image data is in videoNode.Content
 				if ( 'Content' in videoNode ) {