Use the new Elasticsearch client

[delvedor]

As titled.

This pr also removes the aws configuration, since the package has not been updated to support the new client. It introduces two new cli options:

• node: the URL where Elasticsearch is running
• es-version: the major version of Elasticsearch you are using (needed only if ≤7)

It removes host, port, aws-credentials.

The minimum version of Node.js required is v8.

[mcollina]

Failing on Node 12: https://travis-ci.org/pinojs/pino-elasticsearch/jobs/541274020

[delvedor]

I saw that, but the test is passing on my machine. I fear is a timing issue. Can you rerun the CI job?

[delvedor]

Now CI is green. Unfortunately, Travis may cause this flaky tests from time to time.