Change default getDate() to use Date.toISOString()

This patch improves original timestamp by providing a microseconds resolution. Also reduces code by utilizing native method.

From MDN:

The toISOString() method returns a string in ISO format (ISO 8601 Extended Format), which can be described as follows: YYYY-MM-DDTHH:mm:ss.sssZ. The timezone is always UTC as denoted by the suffix "Z".

This is exactly the format required by the syslog protocol: http://www.syslog.cc/ietf/drafts/draft-ietf-syslog-protocol-15.txt