chore/test: use chai#should (hexojs#4902)

Author: SukkaW

.mocharc.yml

@@ -3,6 +3,4 @@ reporter: spec
 ui: bdd
 full-trace: true
 exit: true
-require: 
-  - "chai/register-should"
 parallel: true

test/index.js

@@ -1,6 +1,7 @@
 'use strict';
 
-require('chai');
+const chai = require('chai');
+global.should = chai.should();
 
 describe('Hexo', () => {
   require('./scripts/box');