correct json buffer size optimizations

ZgatewayRFM69.ino

@@ -143,8 +143,7 @@ boolean RFM69toMQTT(void) {
   if (radio.receiveDone())
   {
     trc(F("Creating RFM69 buffer"));
-    const int JSON_MSG_CALC_BUFFER = JSON_OBJECT_SIZE(3);
-    StaticJsonBuffer<JSON_MSG_CALC_BUFFER> jsonBuffer;
+    StaticJsonBuffer<JSON_MSG_BUFFER> jsonBuffer;
     JsonObject& RFM69data = jsonBuffer.createObject();
     uint8_t data[RF69_MAX_DATA_LEN+1]; // For the null character
     uint8_t SENDERID = radio.SENDERID;