Migrator: run pub outdated from the correct directory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
diff --git a/commits.json b/commits.json
index 5803835..87ed3c4 100644
--- a/commits.json
+++ b/commits.json
@@ -1,5 +1,5 @@
 {
   "external/github.com/flutter/engine":"c5d012900f7db0dc5dc9afb46f76d16b87915db0",
   "external/github.com/flutter/flutter":"a1636b6fef2ebe7840ba6dc1b3f9d77095ef3b45",
-  "sdk":"2dea325d871132e84eb9d624ebf7f0fff95c3398"
+  "sdk":"d79c5b5d31d9e3626c32ecaa744e50c6ce6fcb9b"
 }
\ No newline at end of file