Use Node 8 runtime for Lambda

[konklone]

Removes the need for the babel/transpile step in the Lambda function packaging code:

https://aws.amazon.com/blogs/compute/node-js-8-10-runtime-now-available-in-aws-lambda/

and may be able to lower memory usage (and thus cost?):

The new V8 6.0 engine comes with Turbofan and the Ignition pipeline, which leads to lower memory consumption and faster startup time across Node.js applications.