[Docs] Logging format samples outdated

[renshuki]

Description:

Per Beats logs are now ECS-compliant breaking change in 8.0, logging format is now ndjson.

From current Beat - Configure Logging documentation, log samples are still in old format.
Specific sections for reference:

• https://www.elastic.co/guide/en/beats/filebeat/current/configuration-logging.html#_logging_metrics_enabled

2017-12-17T19:17:42.667-0500    INFO    [metrics]       log/log.go:110  Non-zero metrics in the last 30s: beat.info.uptime.ms=30004 beat.memstats.gc_next=5046416

• https://www.elastic.co/guide/en/beats/filebeat/current/configuration-logging.html#_logging_format

2017-12-17T18:54:16.241-0500	INFO	logp/core_test.go:13	unnamed global logger

2017-12-17T18:54:16.242-0500	INFO	[example]	logp/core_test.go:16	some message

2017-12-17T18:54:16.242-0500	INFO	[example]	logp/core_test.go:19	some message	{"x": 1}

As the old logging format is not available since 8.0, it would be great to accomodate this part of the documentation by changing the log samples to the current format.

[botelastic]

Hi!
We just realized that we haven't looked into this issue in a while. We're sorry!

We're labeling this issue as Stale to make it hit our filters and make sure we get back to it as soon as possible. In the meantime, it'd be extremely helpful if you could take a look at it as well and confirm its relevance. A simple comment with a nice emoji will be enough :+1.
Thank you for your contribution!

[botelastic]

Hi!
We just realized that we haven't looked into this issue in a while. We're sorry!

We're labeling this issue as Stale to make it hit our filters and make sure we get back to it as soon as possible. In the meantime, it'd be extremely helpful if you could take a look at it as well and confirm its relevance. A simple comment with a nice emoji will be enough :+1.
Thank you for your contribution!