fix: updated export interval to be 20 seconds instead of 20 milliseco…

…nds (#209)

Updated the METRIC_EXPORT_INTERVAL variable to be 20000 milliseconds, 20 seconds. Fixes issue: #202
---------

cloudrun-malware-scanner/metrics.js

@@ -81,7 +81,7 @@ const COUNTER_ATTRIBUTE_NAMES = {
 const COUNTERS = new Map();
 
 const METRIC_EXPORT_INTERVAL = parseInt(
-  process.env.EXPORT_INTERVAL || '20',
+  process.env.EXPORT_INTERVAL || '20000',
   10,
 );