[improvement] PullRerefresh: use dynamic slot (#2409)

docs/src/demo-common.js

@@ -42,11 +42,11 @@ Locale.add({
     custom: '自定义',
     username: '用户名',
     password: '密码',
-    loading: '加载状态',
     disabled: '禁用状态',
     uneditable: '不可编辑',
     basicUsage: '基础用法',
     advancedUsage: '高级用法',
+    loadingStatus: '加载状态',
     usernamePlaceholder: '请输入用户名',
     passwordPlaceholder: '请输入密码'
   },
@@ -70,7 +70,7 @@ Locale.add({
     custom: 'Custom',
     username: 'Username',
     password: 'Password',
-    loading: 'Loading',
+    loadingStatus: 'Loading',
     disabled: 'Disabled',
     uneditable: 'Uneditable',
     basicUsage: 'Basic Usage',