Revert "Replace callback with throwing error for unsupported glTF version in GLTFLoader"

This reverts commit bbfca2a009a0e16ab4d3306265369304ee832d70.

examples/js/loaders/GLTFLoader.js

@@ -93,7 +93,8 @@ THREE.GLTFLoader = ( function () {
 
 			if ( json.asset === undefined || json.asset.version[ 0 ] < 2 ) {
 
-				throw new Error( 'THREE.GLTFLoader: Unsupported asset. glTF versions >=2.0 are supported.' );
+				onError( new Error( 'THREE.GLTFLoader: Unsupported asset. glTF versions >=2.0 are supported.' ) );
+				return;
 
 			}