Improve the selector for lazy loading images (fix #313)

When `page.dynamic_title` is set to false, the image will not be loaded

Author: cotes2020

_includes/lozad.html

@@ -4,7 +4,7 @@
 <script type="text/javascript" src="https://cdn.jsdelivr.net/npm/lozad/dist/lozad.min.js"></script>
 
 <script type="text/javascript">
-  const imgs = document.querySelectorAll('.post-content img');
+  const imgs = document.querySelectorAll('#main > div.row:first-child > div:first-child img');
   const observer = lozad(imgs);
   observer.observe();
 </script>