Cell content is not strike through with setStrikethrough(true)

[YvesAmmann]

This is:

- [X] a bug report
- [ ] a feature request
- [ ] **not** a usage question (ask them on https://stackoverflow.com/questions/tagged/phpspreadsheet or https://gitter.im/PHPOffice/PhpSpreadsheet)

What is the expected behavior?

Cell content is strike through.

What is the current behavior?

Cell content is not strike through.

What are the steps to reproduce?

<?php
require __DIR__ . '/vendor/autoload.php';

use PhpOffice\PhpSpreadsheet\Spreadsheet;
use PhpOffice\PhpSpreadsheet\Writer\Xlsx;
use PhpOffice\PhpSpreadsheet\Style\Fill;
use PhpOffice\PhpSpreadsheet\Style\Color;
use PhpOffice\PhpSpreadsheet\Style\Alignment;

$excel = new Spreadsheet();
$sheet = $excel->getActiveSheet();
$sheet->setTitle('Test');

$sheet->setCellValue('A1', 'Test setStrikethrough()');
$sheet->getStyle('A1')->getFont()->setStrikethrough(true);

Which versions of PhpSpreadsheet and PHP are affected?

PhpSpreadsheet 1.1
PHP 7.2.2