README Launch Stack Button Points to Outdated .yaml in S3

[Physium]

Describe the bug
When I triggered launch stack from README, it points to https://s3.amazonaws.com/aws-bookstore-demo-app-us-east-1/master-fullstack.yaml which throws the error as mentioned in this PR here. Since the issue it fix, perhaps an update to the yaml in the s3 bucket with the latest changes would really help folks who are trying out for the first time.