uses official s3 repo for download ecs anywhere installation script

[allamand]

Signed-off-by: Sébastien Allamand sebastien@allamand.com

This is adapted with the command generated by the console when adding an external host

[adamjkeller]

Hello, and thank you for the pull request! This repo has been moved to: https://github.com/aws-containers/ecsworkshop

Could you please close and resubmit there?

Thanks!