breadcrumb: add test (#629)

test/unit/specs/breadcrumb.spec.js

+import { createVue } from '../util';
+
+describe('Breadcrumb', () => {
+  it('create', done => {
+    const vm = createVue(`
+      <el-breadcrumb separator=">">
+        <el-breadcrumb-item to="/">首页</el-breadcrumb-item>
+        <el-breadcrumb-item>活动管理</el-breadcrumb-item>
+        <el-breadcrumb-item>活动列表</el-breadcrumb-item>
+        <el-breadcrumb-item>活动详情</el-breadcrumb-item>
+      </el-breadcrumb>
+    `);
+    vm.$nextTick(_ => {
+      expect(vm.$el.querySelector('.el-breadcrumb__separator').innerText).to.equal('>');
+      done();
+    });
+  });
+});