fix(guide): dont-block-the-event-loop.md (#2597)

* Update dont-block-the-event-loop.md

incorrect example code

* fix(guide): dont-block-the-event-loop.md of zh-ch translation

locale/en/docs/guides/dont-block-the-event-loop.md

@@ -255,19 +255,19 @@ Example: JSON blocking. We create an object `obj` of size 2^21 and `JSON.stringi
 var obj = { a: 1 };
 var niter = 20;
 
-var before, res, took;
+var before, str, pos, res, took;
 
 for (var i = 0; i < niter; i++) {
   obj = { obj1: obj, obj2: obj }; // Doubles in size each iter
 }
 
 before = process.hrtime();
-res = JSON.stringify(obj);
+str = JSON.stringify(obj);
 took = process.hrtime(before);
 console.log('JSON.stringify took ' + took);
 
 before = process.hrtime();
-res = str.indexOf('nomatch');
+pos = str.indexOf('nomatch');
 took = process.hrtime(before);
 console.log('Pure indexof took ' + took);
 

locale/zh-cn/docs/guides/dont-block-the-event-loop.md

@@ -256,19 +256,19 @@ app.get('/redos-me', (req, res) => {
 var obj = { a: 1 };
 var niter = 20;
 
-var before, res, took;
+var before, str, pos, res, took;
 
 for (var i = 0; i < niter; i++) {
   obj = { obj1: obj, obj2: obj }; // 每个循环里面将对象 size 加倍
 }
 
 before = process.hrtime();
-res = JSON.stringify(obj);
+str = JSON.stringify(obj);
 took = process.hrtime(before);
 console.log('JSON.stringify took ' + took);
 
 before = process.hrtime();
-res = str.indexOf('nomatch');
+pos = str.indexOf('nomatch');
 took = process.hrtime(before);
 console.log('Pure indexof took ' + took);