handler function in examples is missing callback parameter

[massi-ang]

In all examples, but invokee.js in the LambdaInvoke folder, the handler function misses the callback parameter. While the example work, the lambda function crashes with SIGTERM error just after the handler is invoked.

Adding the callback and invoking it before returning according to https://docs.aws.amazon.com/lambda/latest/dg/nodejs-prog-model-handler.html solves the issue.