doc: update component cover

components/affix/index.en-US.md

@@ -2,7 +2,7 @@
 category: Components
 type: Navigation
 title: Affix
-cover: https://gw.alipayobjects.com/zos/alicdn/tX6-md4H6/Affix.svg
+cover: https://mdn.alipayobjects.com/huamei_7uahnr/afts/img/A*YSm4RI3iOJ8AAAAAAAAAAAAADrJ8AQ/original
 ---
 
 Wrap Affix around another component to make it stick the viewport.

components/affix/index.zh-CN.md

@@ -3,7 +3,7 @@ category: Components
 subtitle: 固钉
 type: 导航
 title: Affix
-cover: https://gw.alipayobjects.com/zos/alicdn/tX6-md4H6/Affix.svg
+cover: https://mdn.alipayobjects.com/huamei_7uahnr/afts/img/A*YSm4RI3iOJ8AAAAAAAAAAAAADrJ8AQ/original
 ---
 
 将页面元素钉在可视范围。

components/alert/index.en-US.md

@@ -2,7 +2,7 @@
 category: Components
 type: Feedback
 title: Alert
-cover: https://gw.alipayobjects.com/zos/alicdn/8emPa3fjl/Alert.svg
+cover: https://mdn.alipayobjects.com/huamei_7uahnr/afts/img/A*Ct7bT7rrTTAAAAAAAAAAAAAADrJ8AQ/original
 ---
 
 Alert component for feedback.

components/alert/index.zh-CN.md

@@ -3,7 +3,7 @@ category: Components
 type: 反馈
 title: Alert
 subtitle: 警告提示
-cover: https://gw.alipayobjects.com/zos/alicdn/8emPa3fjl/Alert.svg
+cover: https://mdn.alipayobjects.com/huamei_7uahnr/afts/img/A*Ct7bT7rrTTAAAAAAAAAAAAAADrJ8AQ/original
 ---
 
 警告提示，展现需要关注的信息。

components/spin/index.zh-CN.md

@@ -3,7 +3,7 @@ category: Components
 type: 反馈
 title: Spin
 subtitle: 加载中
-cover: https://gw.alipayobjects.com/zos/alicdn/8emPa3fjl/Alert.svg
+cover: https://gw.alipayobjects.com/zos/alicdn/8emPa3fjl/Spin.svg
 ---
 
 用于页面和区块的加载中状态。