changed(metric, value, labels, timestamp) {
		this.dirty = true;
		if (Array.isArray(this.reporter))
			this.reporter.forEach(reporter =>
				reporter.metricChanged(metric, value, labels, timestamp)
			);
	}
Some metric has been changed.

@param {BaseMetric} metric
@param {any} value
@param {Object} labels
@param {Number?} timestamp

@memberof MetricRegistry