fix(layout): Make author image url honor baseURL

layouts/partials/avatar.html

 <header class="row text-center header">
-  {{ with .Site.Params.authorimage }} <img src="img/{{ . }}" alt="Author Image" class="img-circle text-center headshot"> {{ end }}
+  {{ with .Site.Params.authorimage }} <img src="/img/{{ . }}" alt="Author Image" class="img-circle text-center headshot"> {{ end }}
   <h1 class="author">{{ .Site.Params.author }}</h1>
 </header>