fetch method
Implementation
@override
Future<Texts> fetch() async {
var applangaResponse = await httpClient.get(
Uri.parse('https://api.applanga.com/v1/api?app=$_appId'),
headers: {HttpHeaders.authorizationHeader: 'Bearer $_apiToken'},
);
var body = jsonDecode(applangaResponse.body);
return _bodyToTexts(body);
}