updete syle with imge format

Author: akoushb

_sass/jekyll-theme-cayman.scss

@@ -404,3 +404,8 @@ a {
 .site-footer-credits {
   color: $blockquote-text-color;
 }
+
+.center-image {
+  display: block;
+  margin: 0 auto;
+}