Fixed setPage return value from int to bool on iOS

[daisuke310vvv]

Hi, I realized that setPage method returns wrong type on iOS.
As you can see below, Android and iOS returns different value and flutter receives as type bool.

// Android
    void setPage(MethodCall call, Result result) {
        if (call.argument("page") != null) {
            int page = (int) call.argument("page");
            pdfView.jumpTo(page);
        }

        result.success(true); // <- Returns value as type `bool`
    }

// iOS
- (void)setPage:(FlutterMethodCall*)call result:(FlutterResult)result {
    NSDictionary<NSString*, NSNumber*>* arguments = [call arguments];
    NSNumber* page = arguments[@"page"];
    
    [_pdfView goToPage: [_pdfView.document pageAtIndex: page.unsignedLongValue ]];
    result(_currentPage); // <- Returns valus as `int`
}

// Flutter

  Future<bool> setPage(int page) async {
    final bool isSet = await _channel.invokeMethod('setPage', <String, dynamic>{
      'page': page,
    });
    return isSet;
  }

then, we crash on iOS when calling setPage

Exception has occurred.
_CastError (type 'int' is not a subtype of type 'bool' in type cast)