需求：下拉框在实现多选的情况下加一个全选，现实全选反选

       <el-select
            v-model="selectData"
            @change="handleSelect"
            collapse-tags
            multiple
            @remove-tag="removeTag"
          >
            <el-option label="全选" :value="0" @click.native="selectAll"></el-option>
            <el-option
              v-for="(item, index) of optionBox.equipState