Migrator: run pub outdated from the correct directory

Fixes https://github.com/dart-lang/sdk/issues/42084

Change-Id: I74eb3cbf61f4346b82f81f77977989fbbd7f8274
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/149366
Commit-Queue: Samuel Rawlins <srawlins@google.com>
Reviewed-by: Janice Collins <jcollins@google.com>

https://dart.googlesource.com/sdk/+/d79c5b5d31d9e3626c32ecaa744e50c6ce6fcb9b
1 file changed
tree: 34c09e283efa207d8ee5c8c7eb51f60e7f78fc7f
  1. commits.json