WebServer examples use an out of date AMI

[joeduffy]

Examples such as https://github.com/pulumi/examples/blob/b2a63a2a9f640882d06f201e26049104e0af3326/aws-js-webserver/index.js#L11 reference an out of date AMI. This is just the JavaScript version but there are multiple aws-xx-webserver projects in this repo for different languages. This AMI has been retired by Amazon so the examples fail. They should use the latest Amazon Linux 2 AMI instead.