Fix: Page model api changes

lib/routes/attachment.js

@@ -61,13 +61,7 @@ module.exports = function(crowi, app) {
           return resolve(pageData);
         });
       } else {
-        Page.findPageById(id, function(err, pageData){
-          if (err) {
-            debug('Page find error', err);
-            return reject(err);
-          }
-          return resolve(pageData);
-        });
+        Page.findPageById(id).then(resolve).catch(reject);
       }
     }).then(function(pageData) {
       page = pageData;