zh-cn: add release schedule (#1892)

1. Add release schedule

2. Current => 当前版

3. Translate maintenance & active

locale/zh-cn/about/releases.md

@@ -2,17 +2,17 @@
 layout: about-release-schedule.hbs
 title: 发布
 statuses:
-  maintenance: 'Maintenance LTS'
-  active: 'Active LTS'
-  current: 'Current'
-  pending: 'Pending'
+  maintenance: '长期维护版'
+  active: '长期支持版(主推)'
+  current: '当前版'
+  pending: '待定'
 columns:
-  - 'Release'
-  - 'Status'
-  - 'Codename'
-  - 'Initial Release'
-  - 'Active LTS Start'
-  - 'Maintenance LTS Start'
-  - 'End-of-life'
-schedule-footer: Dates are subject to change.
+  - '发布'
+  - '状态'
+  - '代号'
+  - '首次发布'
+  - '长期支持版(主推)开始'
+  - '长期维护版开始'
+  - '结束时间'
+schedule-footer: 日期可能会发生变化。
 ---