Change CSS class next_article and previous_article to next-article and previous-article

Fix #70

static/css/elegant.css

@@ -439,11 +439,11 @@ ul.articles-timeline {
     margin: 0;
     padding-bottom: 30px;
 }
-ul.articles-timeline .next_article {
+ul.articles-timeline .next-article {
     float: right;
     margin: 0;
 }
-ul.articles-timeline .previous_article  {
+ul.articles-timeline .previous-article  {
     float: left;
     margin: 0;
 }

templates/article.html

@@ -59,7 +59,7 @@
                         {% set pv_title = ptitle + ' ' +  '<small>' + previous_article.subtitle + '</small>' %}
                         {% set ptitle = ptitle + ' - ' + previous_article.subtitle %}
                     {% endif %}
-                <li class="previous_article">« <a href="{{ SITEURL }}/{{ previous_article.url }}" title="Previous: {{ ptitle }}">{{ pv_title }}</a></li>
+                <li class="previous-article">« <a href="{{ SITEURL }}/{{ previous_article.url }}" title="Previous: {{ ptitle }}">{{ pv_title }}</a></li>
                 {% endif %}
                 {% if next_article %}
                 {% set ntitle = next_article.title|striptags %}
@@ -68,7 +68,7 @@
                         {% set nv_title = ntitle + ' ' +  '<small>' + next_article.subtitle + '</small>' %}
                         {% set ntitle = ntitle + ' - ' + next_article.subtitle %}
                     {% endif %}
-                <li class="next_article"><a href="{{ SITEURL }}/{{ next_article.url }}" title="Next: {{ ntitle }}">{{ nv_title }}</a> »</li>
+                <li class="next-article"><a href="{{ SITEURL }}/{{ next_article.url }}" title="Next: {{ ntitle }}">{{ nv_title }}</a> »</li>
                 {% endif %}
             </ul>
             </nav>