Make the example a bit more Groovy idiomatic (GoogleCloudPlatform#2953)

Author: glaforge

functions/helloworld/groovy-hello-pubsub/src/main/groovy/functions/GroovyHelloPubSub.groovy

@@ -5,7 +5,7 @@ import com.google.cloud.functions.BackgroundFunction
 import com.google.cloud.functions.Context
 import functions.eventpojos.PubSubMessage
 import java.nio.charset.StandardCharsets
-import java.util.logging.Logger;
+import java.util.logging.Logger
 
 class GroovyHelloPubSub implements BackgroundFunction<PubSubMessage> {
     private static final Logger LOGGER = Logger.getLogger(GroovyHelloPubSub.class.name)
@@ -15,11 +15,11 @@ class GroovyHelloPubSub implements BackgroundFunction<PubSubMessage> {
         // name's default value is "world"
         String name = "world"
 
-        if (message?.data != null) {
-             name = new String(Base64.getDecoder().decode(message.data), StandardCharsets.UTF_8)
+        if (message?.data) {
+             name = new String(Base64.decoder.decode(message.data), StandardCharsets.UTF_8)
         }
 
-        LOGGER.info(String.format("Hello %s!", name))
+        LOGGER.info("Hello ${name}!")
         return
     }
 }