Check AWS::Serverless::* resources

> Disable Serverless specs for now
> The main issue here is that CodeUri can be a string or an object, but the format
of the CloudFormation Resource Specification doesn't support specifying
"either or"

https://github.com/jpb/laundry/commit/3d5f42ca859108a72884b0759f5b84a68c6164f1