added missing file to the list

Author: lohanidamodar

src/SDK/Language/Flutter.php

@@ -79,6 +79,12 @@ public function getFiles()
 				'template'      => '/flutter/lib/enums.dart.twig',
 				'minify'        => false,
 			],
+            [
+				'scope'         => 'default',
+				'destination'   => '/lib/exception.dart',
+				'template'      => '/flutter/lib/exception.dart.twig',
+				'minify'        => false,
+			],
             [
                 'scope'         => 'service',
                 'destination'   => '/lib/services/{{service.name | caseDash}}.dart',