docs: update docs/core/metrics.md

Co-authored-by: Sara Gerion <[email protected]>

Author: dreamorosi

Diff for: docs/core/metrics.md

@@ -301,7 +301,7 @@ You can manually flush the metrics with `publishStoredMetrics` as follows:
 
     export const handler = async (_event: any, _context: any) => {
         metrics.addMetric('successfulBooking', MetricUnits.Count, 10);
-        metrics.purgeStoredMetrics();
+        metrics.publishStoredMetrics();
     };
     ```