[Doc] translate theme & demo pages (#320)

* fix: Tabbar icon line-height

* [new feature] progress add showPivot prop

* [new feature] TabItem support vue-router

* [new feature] update document header style

* [Doc] add toast english ducoment

* [bugfix] Search box-sizing wrong

* [Doc] update vant-demo respo

* [Doc] translate theme & demo pages

docs/src/doc.config.js

@@ -308,12 +308,12 @@ module.exports = {
               },
               {
                 path: '/theme',
-                title: 'Theme (In translation)',
+                title: 'Custom Theme',
                 noExample: true
               },
               {
                 path: '/demo',
-                title: 'Demo pages (In translation)',
+                title: 'Demo pages',
                 noDocument: true,
                 noExample: true
               }