rename "Extended Converters" to "Add-on Converters" in navbar

Author: mojavelinux

src/partials/header-content.hbs

@@ -41,7 +41,7 @@
             <a class="navbar-item" href="{{{relativize (resolvePageURL 'asciidoctor.js::index.adoc')}}}">Asciidoctor.js <small>JavaScript</small></a>
             <a class="navbar-item" href="{{{relativize (resolvePageURL 'asciidoctorj::index.adoc')}}}">AsciidoctorJ <small>Java</small></a>
             <hr class="navbar-divider">
-            <div class="navbar-item">Extended Converters</div>
+            <div class="navbar-item">Add-on Converters</div>
             {{!--
             <a class="navbar-item" href="{{{relativize (resolvePageURL 'pdf-converter::index.adoc')}}}">PDF</a>
             <a class="navbar-item" href="{{{relativize (resolvePageURL 'epub3-converter::index.adoc')}}}">EPUB3</a>