[fix] title escaping

searx/engines/stackoverflow.py

     for result in dom.xpath('//div[@class="question-summary search-result"]'):
         link = result.xpath('.//div[@class="result-link"]//a')[0]
         href = urljoin(url, link.attrib.get('href'))
-        title = ' '.join(link.xpath('.//text()'))
+        title = escape(' '.join(link.xpath('.//text()')))
         content = escape(' '.join(result.xpath('.//div[@class="excerpt"]//text()')))
         results.append({'url': href, 'title': title, 'content': content})
     return results