replaced deprecated NodeJs version

Author: Florian

aws-node-auth0-custom-authorizers-api/serverless.yml

@@ -6,7 +6,7 @@ plugins:
 
 provider:
   name: aws
-  runtime: nodejs6.10
+  runtime: nodejs8.10
   region: us-west-2
   environment:
     AUTH0_CLIENT_ID: ${file(./secrets.json):AUTH0_CLIENT_ID}