Fix spotbugs warning about modifiable byte[].

ttnhabbridge/src/main/java/nl/sikken/bertrik/hab/ttn/TtnMessage.java

@@ -55,7 +55,7 @@ public final class TtnMessage {
     }
 
     public byte[] getPayloadRaw() {
-        return payloadRaw;
+        return payloadRaw.clone();
     }
 
     public ObjectNode getPayloadFields() {