Update template.yml to 18 as version 12 node is no longer compatible

Author: medmondson

sample-apps/blank-nodejs/template.yml

@@ -6,7 +6,7 @@ Resources:
     Type: AWS::Serverless::Function
     Properties:
       Handler: index.handler
-      Runtime: nodejs12.x
+      Runtime: nodejs18.x
       CodeUri: function/.
       Description: Call the AWS Lambda API
       Timeout: 10
@@ -25,4 +25,4 @@ Resources:
       Description: Dependencies for the blank sample app.
       ContentUri: lib/.
       CompatibleRuntimes:
-        - nodejs12.x
+        - nodejs18.x