Add subscribers export button class (#743)

closes TryGhost/Ghost#8553
- adds a href for pointer and hover class to subscribers export button

app/templates/subscribers.hbs

@@ -3,7 +3,7 @@
         <h2 class="gh-canvas-title" data-test-screen-title>Subscribers <span style="font-weight:200;margin-left:10px;display:inline-block;" data-test-total-subscribers> ({{total}})</span></h2>
         <div class="view-actions">
             {{#link-to "subscribers.import" class="gh-btn gh-btn-hover-green"}}<span>Import CSV</span>{{/link-to}}
-            <a {{action 'exportData'}} class="gh-btn"><span>Export CSV</span></a>
+            <a href="#" {{action 'exportData'}} class="gh-btn gh-btn-hover-green"><span>Export CSV</span></a>
             {{#link-to "subscribers.new" class="gh-btn gh-btn-green"}}<span>Add Subscriber</span>{{/link-to}}
         </div>
     </header>