解决：`slot` attributes are deprecated.eslint-plugin-vue

用vue3.0做项目是发现：`slot`属性已弃用

但vue 3.0 增加了v-slot的指令，在 <template v-slot:dropdown>就可以了


        <el-dropdown @command="handleCommand">
            <span class="el-dropdown-link">
                下拉菜单
                <i class="el-icon-arrow-down el-icon--right"></i>
            </span>
            <template v-slot:dropdown>
                <el-dropdown-menu>
                <el-dropdown-item icon="el-icon-edit" command="a">修改密码</el-dropdown-item>
                <el-dropdown-item icon="el-icon-user" command="b">退出系统</el-dropdown-item>
            </el-dropdown-menu>
            </template>
        </el-dropdown>