Update .gitignore to new `dart_tool` pub cache

See: https://github.com/dart-lang/sdk/issues/32030
diff --git a/.gitignore b/.gitignore
index 76b960e..3309868 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,7 +1,7 @@
 .buildlog
 .DS_Store
 .idea
-.pub/
+.dart_tool
 .project
 .settings
 build/