feat(List): add error slot

src/list/test/__snapshots__/index.spec.js.snap

@@ -1,5 +1,12 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`error slot 1`] = `
+<div role="feed" class="van-list">
+  <div class="van-list__error-text">Custom Error</div>
+  <div class="van-list__placeholder"></div>
+</div>
+`;
+
 exports[`finished slot 1`] = `
 <div role="feed" class="van-list">
   <div class="van-list__finished-text">Custom Finished</div>

src/list/test/index.spec.js

@@ -83,6 +83,19 @@ test('finished slot', async () => {
   expect(wrapper).toMatchSnapshot();
 });
 
+test('error slot', async () => {
+  const wrapper = mount(List, {
+    propsData: {
+      error: true
+    },
+    scopedSlots: {
+      error: () => 'Custom Error'
+    }
+  });
+
+  expect(wrapper).toMatchSnapshot();
+});
+
 test('immediate check false', async () => {
   const wrapper = mount(List, {
     propsData: {