[Improvement] Tab animation fluency && position (#379)

docs/demos/views/tab.vue

@@ -2,7 +2,7 @@
   <demo-section>
     <demo-block :title="$t('basicUsage')">
       <van-tabs :active="active">
-        <van-tab :title="$t('tab') + index" v-for="index in 4" :key="index">
+        <van-tab :title="$t('tab') + index" v-for="index in tabs" :key="index">
           {{ $t('content') }} {{ index }}
         </van-tab>
       </van-tabs>
@@ -64,7 +64,8 @@ export default {
 
   data() {
     return {
-      active: 2
+      active: 2,
+      tabs: [1, 2, 3, 4]
     };
   },
 

docs/markdown/en-US/tab.md

@@ -106,7 +106,7 @@ export default {
 |-----------|-----------|-----------|-------------|-------------|
 | type | There are two style tabs, set this attribute to change tab style | `String` | `line` | `card` |
 | active | Index of active tab | `String` `Number` | `0` | - |
-| duration | Toggle tab's animation time | `Number` | `0.3` | - | - |
+| duration | Toggle tab's animation time | `Number` | `0.2` | - | - |
 | swipeThreshold | Set swipe tabs threshold | `Number` | `4` | - | - |
 
 ### Tab API

docs/markdown/zh-CN/tab.md

@@ -106,7 +106,7 @@ export default {
 |-----------|-----------|-----------|-------------|-------------|
 | type | Tab 样式类型 | `String` | `line` | `card` |
 | active | 默认激活的 tab | `String` `Number` | `0` | - |
-| duration | 切换 tab 的动画时间 | `Number` | `0.3` | - | - |
+| duration | 切换 tab 的动画时间 | `Number` | `0.2` | - | - |
 | swipeThreshold | 滚动阀值，设置 Tab 超过多少个可滚动 | `Number` | `4` | - | - |
 
 ### Tab API