Fix parsing of returned json object.

The json object now has multiple values in data{}. Changing the code to pull the "last" value.

Author: ed7coyne

examples/FirebaseStream_ESP8266/FirebaseStream_ESP8266.ino

@@ -65,7 +65,7 @@ void loop() {
        Serial.println(event);
        JsonObject& json = buf.parseObject((char*)event.c_str());
        String path = json["path"];
-       float data = json["data"];       
+       float data = json["data"]["last"];       
 
        // TODO(proppy): parse JSON object.
        display.clearDisplay();