[bugfix] Panel: header-class not work (#831)

packages/panel/index.ts

@@ -1,13 +1,12 @@
 import { VantComponent } from '../common/component';
 
 VantComponent({
-  classes: ['footer-class'],
+  classes: ['header-class', 'footer-class'],
 
   props: {
     desc: String,
     title: String,
     status: String,
-    headerClass: String,
     useFooterSlot: Boolean
   }
 });

packages/panel/index.wxml

@@ -4,7 +4,7 @@
     title="{{ title }}"
     label="{{ desc }}"
     value="{{ status }}"
-    custom-class="{{ headerClass }}"
+    custom-class="header-class"
     value-class="van-panel__header-value"
   />
   <slot wx:else name="header" />