fix eslint error in gen-single-config.js

build/gen-single-config.js

 var path = require('path');
 var config = require('./config');
 
-module.exports = function (context, moduleName, entry) {
+module.exports = function(context, moduleName, entry) {
   return {
     entry: {
       index: path.resolve(context, entry || 'index.js')
@@ -13,5 +13,5 @@ module.exports = function (context, moduleName, entry) {
     extends: ['vue2'],
     alias: config.alias,
     externals: { vue: config.vue }
-  }
-}
+  };
+};