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/docs/reference/glossary/horizontal-pod-autoscaler.md

@@ -0,0 +1,42 @@
+---
+title: Pod 水平自动扩缩器（Horizontal Pod Autoscaler）
+id: horizontal-pod-autoscaler
+date: 2018-04-12
+full_link: /zh/docs/tasks/run-application/horizontal-pod-autoscale/
+short_description: >
+  Pod 水平自动扩缩器（Horizontal Pod Autoscaler）是一种 API 资源，它根据目标 CPU 利用率或自定义度量目标扩缩 Pod 副本的数量。
+
+aka: 
+- HPA
+tags:
+- operation
+---
+
+<!--
+---
+title: Horizontal Pod Autoscaler
+id: horizontal-pod-autoscaler
+date: 2018-04-12
+full_link: /docs/tasks/run-application/horizontal-pod-autoscale/
+short_description: >
+  An API resource that automatically scales the number of pod replicas based on targeted CPU utilization or custom metric targets.
+
+aka: 
+- HPA
+tags:
+- operation
+---
+-->
+
+ Horizontal Pod Autoscaler（Pod 水平自动扩缩器）是一种 API 资源，它根据目标 CPU 利用率或自定义度量目标扩缩 Pod 副本的数量。
+
+<!--more--> 
+
+<!--
+HPA is typically used with {{< glossary_tooltip text="ReplicationControllers" term_id="replication-controller" >}}, {{< glossary_tooltip text="Deployments" term_id="deployment" >}}, or {{< glossary_tooltip text="ReplicaSets" term_id="replica-set" >}}. It cannot be applied to objects that cannot be scaled, for example {{< glossary_tooltip text="DaemonSets" term_id="daemonset" >}}.
+-->
+
+HPA 通常用于 {{< glossary_tooltip text="ReplicationControllers" term_id="replication-controller" >}}
+、{{< glossary_tooltip text="Deployments" term_id="deployment" >}} 
+或者 {{< glossary_tooltip text="ReplicaSets" term_id="replica-set" >}} 上。
+HPA 不能用于不支持扩缩的对象，例如 {{< glossary_tooltip text="DaemonSets" term_id="daemonset" >}}。