- Update expected string in pub test.

BUG=

Review URL: https://codereview.chromium.org//1159983005

test/transformer/fails_to_load_a_transform_with_an_import_error_test.dart

@@ -31,7 +31,7 @@ main() {
       var pub = startPubServe();
       pub.stderr.expect("Unhandled exception:");
       pub.stderr.expect(
-          startsWith("Uncaught Error: Load Error: Failure getting "));
+          startsWith("Load Error for "));
       pub.shouldExit(1);
     });
   });