Replace deprecated StaticJsonDocument type

src/wlan.cpp

@@ -39,7 +39,7 @@ void disconnect_mqtt(PubSubClient &client, const char *topic) {
 }
 
 size_t construct_json(float *data, char *buffer, int buffer_size) {
-  StaticJsonDocument<100> json;
+  JsonDocument json;
   json["temperature"] = data[0];
   json["humidity"] = data[1];
   size_t payload_size = serializeJson(json, buffer, buffer_size);