refactor: server code (#2545)

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

server/core/db.js

@@ -43,8 +43,7 @@ module.exports = {
     let sslOptions = null
     if (dbUseSSL && _.isPlainObject(dbConfig) && _.get(WIKI.config.db, 'sslOptions.auto', null) === false) {
       sslOptions = WIKI.config.db.sslOptions
-      // eslint-disable-next-line no-unneeded-ternary
-      sslOptions.rejectUnauthorized = sslOptions.rejectUnauthorized === false ? false : true
+      sslOptions.rejectUnauthorized = sslOptions.rejectUnauthorized !== false
       if (sslOptions.ca && sslOptions.ca.indexOf('-----') !== 0) {
         sslOptions.ca = fs.readFileSync(path.resolve(WIKI.ROOTPATH, sslOptions.ca))
       }