bump the node runtime to node14.x

[fblecha]

either bump the doc to the newest runtime or put a link to the lambda runtimes (https://docs.aws.amazon.com/lambda/latest/dg/lambda-runtimes.html)

[jayair]

Let's hold off on this one. I'll need to test the sample app with this before making the switch. It'll most likely be fine but worth a test.