getJar method

Implementation

Future<String> getJar() async {
  String dir = path.join(root,'versions/$version_name');
  await createDirIfNotExists(dir);
  if(!await File('$dir/$version_name.jar').exists()) await downloadFile(this.version["downloads"]["client"]["url"], '$dir/$version_name.jar');
  if(!await File('$dir/$version_name.json').exists()) await File('$dir/$version_name.json').writeAsString(JsonEncoder.withIndent('  ').convert(this.version));
  return resolvePath('$dir/$version_name.jar');
}