Remove repeated name from author avatar alt

Sets blog author avatar image alt to empty string as it is repeated as text immediately after the image ([alternative text of images should not be repeated as text
](https://dequeuniversity.com/rules/axe/4.10/image-redundant-alt)).

Author: griffenedge

_layouts/post.html

@@ -4,7 +4,7 @@
 <article id="post">
   <h2>{{ page.title }}</h2>
   <h3>{{ page.date | date_to_long_string }}</h3>
-  <h3 class="author"><a href="https://github.com/{{ page.author }}"><img class="avatar" src="https://avatars2.githubusercontent.com/{{ page.author }}?v=3&amp;s=80" alt="{{ page.author }}" width="40" height="40">{{ page.author }}</a></h3>
+  <h3 class="author"><a href="https://github.com/{{ page.author }}"><img class="avatar" src="https://avatars2.githubusercontent.com/{{ page.author }}?v=3&amp;s=80" alt="" width="40" height="40">{{ page.author }}</a></h3>
   <div class="postcontent singlepostcontent">
     {{ content }}