Fix encoding of argument in test

Author: sigurdm

test/add/common/add_test.dart

@@ -2,8 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'dart:io' show File;
 import 'dart:convert';
+import 'dart:io' show File;
 
 import 'package:path/path.dart' as p;
 import 'package:pub/src/exit_codes.dart' as exit_codes;
@@ -1192,9 +1192,11 @@ dependency_overrides:
 
     // Explicitly add using a forward slash in absolute path.
     // This should be preserved in the pubspec.yaml, even on windows.
-    await pubAdd(args: ['foo:${json.encode(
-      {'path': '$sandbox/foo'}
-    )}']);
+    await pubAdd(
+      args: [
+        'foo:${json.encode({'path': '$sandbox/foo'})}',
+      ],
+    );
 
     await d
         .appDir(