Merge pull request #501 from DominusKelvin/feat/add-appName-to-constants

[feat] add appName to whitelisted connection options

Author: DominusKelvin

lib/private/constants/config-whitelist.constant.js

@@ -29,6 +29,6 @@ module.exports = [
   'authMechanism', 'compression', 'fsync', 'readPreferenceTags', 'numberOfRetries',
   'auto_reconnect', 'monitorCommands', 'minSize', 'useNewUrlParser', 'useUnifiedTopology',
   'localThresholdMS', 'serverSelectionTimeoutMS', 'heartbeatFrequencyMS', 'autoEncryption',
-  'driverInfo'
+  'driverInfo', 'appName'
 
 ];