Remove the empty subtitle attributes and if not present use the abstract of the content.

Signed-off-by: James R. Perkins <jperkins@ibm.com>

Author: jamezp

content/blogs/index.html

@@ -16,6 +16,8 @@
                 <h3 class="card-title post-title">{post.title}</h3>
                 {#if post.data.containsKey('subtitle')}
                 <h5 class="post-subtitle text-muted">{post.data.subtitle}</h5>
+                {#else}
+                <h5 class="post-subtitle text-muted">{post.contentAbstract}</h5>
                 {/if}
             </a>
             <div class="post-meta">