feat(Dialog): update border radius (#2158)

example/pages/dialog/index.wxml

@@ -1,48 +1,26 @@
 <demo-block title="提示弹窗" padding>
-  <van-button
-    plain
-    type="primary"
-    class="demo-margin-right"
-    bind:click="onClickAlert"
-  >
+  <van-button type="primary" class="demo-margin-right" bind:click="onClickAlert">
     提示弹窗
   </van-button>
-  <van-button
-    plain
-    type="primary"
-    bind:click="onClickAlert2"
-  >
+  <van-button type="primary" bind:click="onClickAlert2">
     提示弹窗（无标题）
   </van-button>
 </demo-block>
 
 <demo-block title="确认弹窗" padding>
-  <van-button
-    plain
-    type="primary"
-    bind:click="onClickConfirm"
-  >
+  <van-button type="primary" bind:click="onClickConfirm">
     确认弹窗
   </van-button>
 </demo-block>
 
 <demo-block title="异步关闭" padding>
-  <van-button
-    plain
-    type="primary"
-    bind:click="onClickAsyncClose"
-  >
+  <van-button type="primary" bind:click="onClickAsyncClose">
     异步关闭
   </van-button>
 </demo-block>
 
 <demo-block title="组件调用" padding>
-  <van-button
-    plain
-    type="danger"
-    class="demo-margin-right"
-    bind:click="showCustomDialog"
-  >
+  <van-button type="primary" class="demo-margin-right" bind:click="showCustomDialog">
     组件调用
   </van-button>
   <van-dialog

example/pages/dialog/index.wxss

@@ -1,5 +1,5 @@
 .demo-image {
+  box-sizing: border-box;
   width: 100%;
   padding: 25px 20px 0;
-  box-sizing: border-box;
 }

packages/dialog/index.less

@@ -6,7 +6,7 @@
   width: 320px;
   overflow: hidden;
   font-size: 16px;
-  border-radius: 4px;
+  border-radius: 16px;
   .theme(background-color, '@white');
 
   @media (max-width: 321px) {