Chroe: Fix something in articles (#3349)

1) For 'cookie-and-session.md', fix the icon, to make it the same as
"Error".
2) For 'cluster-and-ipc.md', Merge the two pharagraphs together, and
for the Chinese version, translate the English part into Chinese.'

docs/source/en/core/cluster-and-ipc.md

@@ -5,10 +5,10 @@ We know that JavaScript codes are run on single thread, in other words, one Node
 
 > how to squeeze all server resources, taking advantages of multi-cores?
 
-And the official solution provided by Node.js is [Cluster module](https://nodejs.org/api/cluster.html)
+And the official solution provided by Node.js is [Cluster module](https://nodejs.org/api/cluster.html), and there's an introduction:
 
 > A single instance of Node.js runs in a single thread. To take advantage of multi-core systems the user will sometimes want to launch a cluster of Node.js processes to handle the load.
-
+>
 > The cluster module allows you to easily create child processes that all share server ports.
 
 # What is Cluster?

docs/source/en/core/cookie-and-session.md

@@ -164,7 +164,7 @@ What you need to pay special attention to is that you need to avoid the followin
 ctx.session._visited = 1;   //   --> property will lost
 ctx.session.isNew = 'HeHe'; //   --> session keyword, should not write it
 
-// ✅ Right way
+// ✔️ Right way
 ctx.session.visited = 1;    //   -->  Everything is all right
 ```
 

docs/source/zh-cn/core/cluster-and-ipc.md

@@ -5,11 +5,11 @@ title: 多进程模型和进程间通讯
 
 > 如何榨干服务器资源，利用上多核 CPU 的并发优势？
 
-而 Node.js 官方提供的解决方案是 [Cluster 模块](https://nodejs.org/api/cluster.html)
+而 Node.js 官方提供的解决方案是 [Cluster 模块](https://nodejs.org/api/cluster.html)，其中包含一段简介：
 
-> A single instance of Node.js runs in a single thread. To take advantage of multi-core systems the user will sometimes want to launch a cluster of Node.js processes to handle the load.
-
-> The cluster module allows you to easily create child processes that all share server ports.
+> 单个 Node.js 实例在单线程环境下运行。为了更好地利用多核环境，用户有时希望启动一批 Node.js 进程用于加载。
+>
+> 集群化模块使得你很方便地创建子进程，以便于在服务端口之间共享。
 
 ## Cluster 是什么呢？
 

docs/source/zh-cn/core/cookie-and-session.md

@@ -140,7 +140,7 @@ ctx.session = null;
 ctx.session._visited = 1;   //    --> 该字段会在下一次请求时丢失
 ctx.session.isNew = 'HeHe'; //    --> 为内部关键字, 不应该去更改
 
-// ✅ 正确的用法
+// ✔️ 正确的用法
 ctx.session.visited = 1;    //   -->  此处没有问题
 ```