Badge: add hidden prop, close #2042 (#2050)

examples/docs/en-US/badge.md

@@ -135,3 +135,4 @@ Use a red dot to mark content that needs to be noticed.
 | value          | display value      | string, number          |          —             |    —     |
 | max          |  maximum value, shows '{max}+' when exceeded. Only works if `value` is a `Number`   | number  |         —              |     —    |
 | is-dot       | if a little dot is displayed   | boolean  |  —  |  false |
+| hidden | hidden badge | boolean | - | false |

examples/docs/zh-CN/badge.md

@@ -137,3 +137,4 @@
 | value          | 显示值      | string, number          |          —             |    —     |
 | max          |  最大值，超过最大值会显示 '{max}+'，要求 value 是 Number 类型    | number  |         —              |     —    |
 | is-dot       | 小圆点    | boolean  |  —  |  false |
+| hidden | 隐藏 badge | boolean | - | false |

packages/badge/src/main.vue

 <template>
   <div class="el-badge">
     <slot></slot>
+    <transition name="el-zoom-in-center">
       <sup
+        v-show="!hidden"
         v-text="content"
         class="el-badge__content"
         :class="{ 'is-fixed': $slots.default, 'is-dot': isDot }">
       </sup>
+    </transition>
   </div>
 </template>
 
@@ -16,7 +19,8 @@ export default {
   props: {
     value: {},
     max: Number,
-    isDot: Boolean
+    isDot: Boolean,
+    hidden: Boolean
   },
 
   computed: {