docs: make sure Javascript links to latest stable by default

docs/processors/version-data.js

@@ -37,7 +37,9 @@ module.exports = {
     });
     extraData.version = {
       list: versions,
-      current: _.find(versions, { name: currentVersion })
+      current: _.find(versions, { name: currentVersion }),
+      //Stable = most recent (first) valid semver version
+      stable: _.find(versions, function(v) { return semver.valid(v.name); })
     };
   }
 };

docs/templates/pages-data.template.html

@@ -49,7 +49,7 @@
             <!-- Docs: JavaScript -->
             <ul class="nav left-menu active-menu">
               <li class="menu-title">
-                <a href="{% if page.versionHref %}{{page.versionHref}}{% else %}{{site.docs_latest}}{% endif %}">
+              <a href="{% if page.versionHref %}{{page.versionHref}}{% else %}}<$ version.stable.href $>{% endif %}">
                   JavaScript
                 </a>
               </li>