publishing validation warning

[devoncarew]

We see a publishing warning from this package:

Package validation found the following potential issue:
  * The name of "lib/builder.dart", "builder", should match the name of the package, "shelf_router_generator".
    This helps users know what library to import.

This is causes the publishing check to fail for all PRs to this repo. We should either address this warning or do something like parameterize the publishing check to detect and validate changed packages.

[devoncarew]

closing in favor of dart-lang/pub#4484