Additional fixes to new notification docs

chrome/common/extensions/docs/templates/json/extensions_sidenav.json

 [
   {
     "title": "Getting Started",
     "fileName": "getstarted.html"
   },
   {
     "title": "Overview",
     "fileName": "overview.html"
   },
   {
@@ skipping 11 matching lines @@
           {
             "title": "Browser Actions",
             "fileName": "browserAction.html"
           },
           {
             "title": "Context Menus",
             "fileName": "contextMenus.html"
           },
           {
             "title": "Desktop Notifications",
-            "fileName": "notifications.html"
+            "fileName": "desktop_notifications.html"
           },
           {
             "title": "Omnibox",
             "fileName": "omnibox.html"
           },
           {
             "title": "Options Pages",
             "fileName": "options.html"
           },
           {
@@ skipping 166 matching lines @@
         "title": "Hosted Apps",
         "fileName": "http://code.google.com/chrome/apps/docs/developers_guide.html"
       },
       {
         "title": "Themes",
         "fileName": "themes.html"
       }
     ]
   }
 ]