fix: svg support old broswer

https://github.com/PanJiaChen/vue-element-admin/commit/6eccffeb2f9037e873591944e119d0246139ffc7

src/components/SvgIcon/index.vue

@@ -1,7 +1,7 @@
 <template>
   <div v-if="isExternal" :style="styleExternalIcon" class="svg-external-icon svg-icon" v-on="$listeners" />
   <svg v-else :class="svgClass" aria-hidden="true" v-on="$listeners">
-    <use :href="iconName" />
+    <use :xlink:href="iconName" />
   </svg>
 </template>