Client does not trigger events

[pavel-si]

	Type:        "trigger", 
	ServiceKey:  <token>,
	Description: <message>,
}
pagerduty.CreateEvent(event)

does not trigger the alert because json tags on Event do not match the required format here: https://v2.developer.pagerduty.com/docs/send-an-event-events-api-v2

[tmccleve]

This package is currently using the v2 api, but v1 events. See https://v2.developer.pagerduty.com/docs/trigger-events

Line referencing v1 events https://github.com/PagerDuty/go-pagerduty/blob/master/event.go#L10

Both #83 and #100 are both centric to v2 event support.