[new feature] Icon: size prop support number type

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

@@ -15,6 +15,11 @@ exports[`render icon with url name 1`] = `
   <!----></i>
 `;
 
+exports[`size without unit 1`] = `
+<i class="van-icon van-icon-undefined" style="font-size: 20px;">
+  <!----></i>
+`;
+
 exports[`tag prop 1`] = `
 <div class="van-icon van-icon-undefined">
   <!---->

packages/icon/test/index.spec.js

@@ -36,3 +36,12 @@ test('tag prop', () => {
   });
   expect(wrapper).toMatchSnapshot();
 });
+
+test('size without unit', () => {
+  const wrapper = mount(Icon, {
+    propsData: {
+      size: 20
+    }
+  });
+  expect(wrapper).toMatchSnapshot();
+});