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/member.md

@@ -0,0 +1,42 @@
+---
+title: 成员（Member）
+id: member
+date: 2018-04-12
+full_link: 
+short_description: >
+  K8s 社区中持续活跃的贡献者。
+
+aka: 
+tags:
+- community
+---
+
+<!--
+---
+title: Member
+id: member
+date: 2018-04-12
+full_link: 
+short_description: >
+  A continuously active contributor in the K8s community.
+
+aka: 
+tags:
+- community
+---
+-->
+
+<!--
+ A continuously active {{< glossary_tooltip text="contributor" term_id="contributor" >}} in the K8s community.
+-->
+
+ K8s 社区中持续活跃的{{< glossary_tooltip text="贡献者（contributor）" term_id="contributor" >}}。
+
+<!--more--> 
+
+<!--
+Members can have issues and PRs assigned to them and participate in {{< glossary_tooltip text="special interest groups (SIGs)" term_id="sig" >}} through GitHub teams. Pre-submit tests are automatically run for members' PRs. A member is expected to remain an active contributor to the community.
+-->
+
+可以将问题单（issue）和 PR 指派给成员（Member），成员（Member）也可以通过 GitHub 小组加入 {{< glossary_tooltip text="特别兴趣小组 (SIGs)" term_id="sig" >}}。针对成员（Member）所提交的 PR，系统自动运行提交前测试。成员（Member）应该是持续活跃的社区贡献者。
+