feat(PullRefresh): add success slot

src/pull-refresh/test/__snapshots__/demo.spec.js.snap

@@ -2,11 +2,25 @@
 
 exports[`renders demo correctly 1`] = `
 <div>
-  <div class="van-pull-refresh">
-    <div class="van-pull-refresh__track" style="transition-duration: 0ms;">
-      <div class="van-pull-refresh__head"></div>
-      <div>
-        <p>刷新次数: 0</p>
+  <div class="van-tabs van-tabs--line">
+    <div class="van-tabs__wrap van-hairline--top-bottom">
+      <div role="tablist" class="van-tabs__nav van-tabs__nav--line">
+        <div role="tab" aria-selected="true" class="van-tab van-tab--active van-ellipsis"><span class="van-tab__text">基础用法<!----></span></div>
+        <div role="tab" class="van-tab van-ellipsis"><span class="van-tab__text">刷新成功提示<!----></span></div>
+        <div class="van-tabs__line" style="width: 0px; transform: translateX(0px) translateX(-50%);"></div>
+      </div>
+    </div>
+    <div class="van-tabs__content">
+      <div role="tabpanel" class="van-tab__pane" style="">
+        <div class="van-pull-refresh">
+          <div class="van-pull-refresh__track" style="transition-duration: 0ms;">
+            <div class="van-pull-refresh__head"></div>
+            <p>下拉试试</p>
+          </div>
+        </div>
+      </div>
+      <div role="tabpanel" class="van-tab__pane" style="display: none;">
+        <!---->
       </div>
     </div>
   </div>

src/pull-refresh/test/__snapshots__/index.spec.js.snap

@@ -80,6 +80,14 @@ exports[`not in page top 1`] = `
 </div>
 `;
 
+exports[`render success slot 1`] = `
+<div class="van-pull-refresh">
+  <div class="van-pull-refresh__track" style="transition-duration: 300ms; transform: translate3d(0,50px, 0);">
+    <div class="van-pull-refresh__head">Custom Success</div>
+  </div>
+</div>
+`;
+
 exports[`render success text 1`] = `
 <div class="van-pull-refresh">
   <div class="van-pull-refresh__track" style="transition-duration: 300ms; transform: translate3d(0,50px, 0);">