Errors in the encoding of special characters

* **OS:** macOS Mojave 10.14.6
* **Java:** 1.8.0_192

Example:
```bash
$ java -jar irbench-v0.0.1-beta.2.jar -questions qald-9-train-multilingual -lang en
```
among others, retrieves the question
```json
"question":"Did Kaurism\u00C3\u00A4ki ever win the Grand Prix at Cannes?"
```
where `Kaurismäki` is being encoded incorrectly, since `\u00C3\u00A4` corresponds to `Ã¤` and not to `ä`.