Switch language name 'zh' to 'zh-cn'

This is the first step to rename 'zh' to 'zh-cn'. There are several reasons why we rename the language name.

- The upstream docsy theme changed the language name, leading to many warnings during site build;
  The side-effect is that the i18n strings are no longer working.
- We believe renaming the language is the right thing to do, because this move can make room for other variants of Chinese language, such as 'zh-tw', 'zh-sg' etc.

There would be several follow-ups to this PR, such as fixing the intra-site links, adding redirects etc.

We will lock up changes to zh/zh-cn pages for the moment, until this one gets in.

This PR is based on commit cdad0a7342.

content/zh-cn/blog/_posts/2015-06-00-Slides-Cluster-Management-With.md

@@ -0,0 +1,24 @@
+---
+title: "幻灯片：Kubernetes 集群管理，爱丁堡大学演讲"
+date: 2015-06-26
+slug: slides-cluster-management-with
+---
+
+<!--
+---
+title: " Slides: Cluster Management with Kubernetes, talk given at the University of Edinburgh "
+date: 2015-06-26
+slug: slides-cluster-management-with
+url: /zh/blog/2015/06/Slides-Cluster-Management-With
+---
+-->
+
+<!--
+On Friday 5 June 2015 I gave a talk called [Cluster Management with Kubernetes](https://docs.google.com/presentation/d/1H4ywDb4vAJeg8KEjpYfhNqFSig0Q8e_X5I36kM9S6q0/pub?start=false&loop=false&delayms=3000) to a general audience at the University of Edinburgh. The talk includes an example of a music store system with a Kibana front end UI and an Elasticsearch based back end which helps to make concrete concepts like pods, replication controllers and services.
+
+[Cluster Management with Kubernetes](https://docs.google.com/presentation/d/1H4ywDb4vAJeg8KEjpYfhNqFSig0Q8e_X5I36kM9S6q0/pub?start=false&loop=false&delayms=3000).
+-->
+
+2015年6月5日星期五，我在爱丁堡大学给普通听众做了一个演讲，题目是[使用 Kubernetes 进行集群管理](https://docs.google.com/presentation/d/1H4ywDb4vAJeg8KEjpYfhNqFSig0Q8e_X5I36kM9S6q0/pub?start=false&loop=false&delayms=3000)。这次演讲包括一个带有 Kibana 前端 UI 的音乐存储系统的例子，以及一个基于 Elasticsearch 的后端，该后端有助于生成具体的概念，如 pods、复制控制器和服务。
+
+[Kubernetes 集群管理](https://docs.google.com/presentation/d/1H4ywDb4vAJeg8KEjpYfhNqFSig0Q8e_X5I36kM9S6q0/pub?start=false&loop=false&delayms=3000)。