Show real alternative description on Travis badge

Author: webknjaz

alabaster/about.html

@@ -28,7 +28,7 @@ <h1 class="logo"><a href="{{ pathto(master_doc) }}">{{ project }}</a></h1>
 <p>
 <a class="badge" href="{{ theme_travis_build_url }}">
     <img
-        alt="{{ theme_travis_badge_url }}"
+        alt="Travis CI build badge"
         src="{{ theme_travis_badge_url }}"
     />
 </a>