Fix: 修复toast关闭时未移除Dom节点，以及补上单元测试 (#19)

* 文档页样式和打包配置优化

* upload unit test

* intanbul ignore src/index

* unit test

* utils dom unit test

* fix: toast not remove

* remove dom unit test

* remove toast clear unit test

* remove toast import vue

packages/vant-css/src/toast.css

@@ -51,6 +51,9 @@
   }
 }
 
-.van-toast-fade-enter, .van-toast-fade-leave-active {
+.van-toast-fade-enter-active, .van-toast-fade-leave-active {
+  transition: opacity .2s;
+}
+.van-toast-fade-enter, .van-toast-fade-leave-to {
   opacity: 0;
 }