refactor: server code (#2545)

+ Remove duplicated await
+ Replace some legacy codes with ES6
+ Fix some of eslint problems

server/models/assetFolders.js

@@ -47,8 +47,7 @@ module.exports = class AssetFolder extends Model {
           sqb.select('a.id', 'a.name', 'a.slug', 'a.parentId').from('assetFolders AS a').join('ancestors', 'ancestors.parentId', 'a.id')
         })
       }).select('*').from('ancestors')
-    }
-    else {
+    } else {
       hier = await WIKI.models.knex.withRecursive('ancestors', qb => {
         qb.select('id', 'name', 'slug', 'parentId').from('assetFolders').where('id', folderId).union(sqb => {
           sqb.select('a.id', 'a.name', 'a.slug', 'a.parentId').from('assetFolders AS a').join('ancestors', 'ancestors.parentId', 'a.id')