fixed a small html typo

blockchainCloud_client.html

@@ -600,7 +600,6 @@
         <button onclick="cloudArticleApp.retrieveLatestContent()">Refresh</button>
         <button onclick="cloudArticleApp.logout()">Logout</button>
         <button onclick="cloudArticleApp.reset_export_list()">Reset Export Selection</button>
-        <button onclick="cloudArticleApp."></button>
         <button onclick="cloudArticleApp.export_as_file()">Export Selections as file</button>
     </div>
     <div id="admindiv"></div>