Validator.checkFileNameAndFormat incorrectly assert message

It says that jpeg must end with png
```dart
} else if (format == CompressFormat.png) {
  assert(name.endsWith(".png"), "The jpeg format name must end with png.");
```

See [here](https://github.com/alann-maulana/image_compression_flutter/blob/fb9880f174f4d71384caa44df8e846808b400fcc/lib/src/validator.dart#L25)