Fix another transformer load error test.

sdk/lib/_internal/pub/test/transformer/fails_to_load_a_transform_with_an_import_error_test.dart

Index: sdk/lib/_internal/pub/test/transformer/fails_to_load_a_transform_with_an_import_error_test.dart
diff --git a/sdk/lib/_internal/pub/test/transformer/fails_to_load_a_transform_with_an_import_error_test.dart b/sdk/lib/_internal/pub/test/transformer/fails_to_load_a_transform_with_an_import_error_test.dart
index 5e68175ed0dc14d098b9c8a8a07e3ef9cbd9d80a..6f910421ed844cf452b973a1d67fafe1f34ec0d4 100644
--- a/sdk/lib/_internal/pub/test/transformer/fails_to_load_a_transform_with_an_import_error_test.dart
+++ b/sdk/lib/_internal/pub/test/transformer/fails_to_load_a_transform_with_an_import_error_test.dart
@@ -28,7 +28,8 @@ main() {
 
     createLockFile('myapp', pkg: ['barback']);
     var pub = startPubServe();
-    pub.stderr.expect(endsWith("error: line 1 pos 1: library handler failed"));
+    pub.stderr.expect("'Unhandled exception:");
+    pub.stderr.expect(startsWith("Failure getting "));
     pub.shouldExit(1);
   });
 }