[new feature] Uploader: add max-count prop

packages/uploader/test/__snapshots__/demo.spec.js.snap

@@ -10,6 +10,14 @@ exports[`renders demo correctly 1`] = `
       </div>
     </div>
   </div>
+  <div>
+    <div class="van-uploader">
+      <div class="van-uploader__wrapper">
+        <div class="van-uploader__upload"><i class="van-icon van-icon-plus van-uploader__upload-icon">
+            <!----></i><input multiple="multiple" type="file" accept="image/*" class="van-uploader__input"></div>
+      </div>
+    </div>
+  </div>
   <div>
     <div class="van-uploader">
       <div class="van-uploader__wrapper">

packages/uploader/test/__snapshots__/index.spec.js.snap

@@ -1,5 +1,16 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`max-count prop 1`] = `
+<div class="van-uploader">
+  <div class="van-uploader__wrapper">
+    <div class="van-image van-uploader__preview"><img src="test" class="van-image__img" style="object-fit: cover;">
+      <div class="van-image__loading"><i class="van-icon van-icon-photo-o" style="font-size: 22px;">
+          <!----></i></div>
+    </div>
+  </div>
+</div>
+`;
+
 exports[`render preview image 1`] = `
 <div class="van-uploader">
   <div class="van-uploader__wrapper">

packages/uploader/test/index.spec.js

@@ -136,3 +136,17 @@ it('render preview image', async () => {
 
   expect(wrapper).toMatchSnapshot();
 });
+
+it('max-count prop', async () => {
+  const wrapper = mount(Uploader, {
+    propsData: {
+      preview: true,
+      maxCount: 1
+    }
+  });
+
+  wrapper.vm.onChange(multiFile);
+  await later();
+
+  expect(wrapper).toMatchSnapshot();
+});