Update docs/core/metrics.md

Co-authored-by: Florian Chazal <florianchazal@gmail.com>

Author: saragerion

docs/core/metrics.md

@@ -145,7 +145,7 @@ See examples below:
     import { Context } from 'aws-lambda';
     import middy from '@middy/core';
 
-    const metrics = new Metrics({namespace:"serverlessAirline", service:"orders"});
+    const metrics = new Metrics({ namespace: 'serverlessAirline', service: 'orders' });
 
     const lambdaHandler = async (event: any, context: Context) => {
         metrics.addMetric('successfulBooking', MetricUnits.Count, 1);