elementui upload上传单个文件可覆盖文件

<el-upload
          action="#"
          list-type="picture"
          :auto-upload="false"
          :on-change="changeImg"
          :limit="1"
          :file-list="fileList"
          :on-exceed="handleExceed"
          ref="rebateUpload"
  >
        <el-button
               slot="trigger"
               size="big"
               class="mdc-button mdc-button--unelevated mdc-ripple-upgraded"
       >重新上传</el-button>
</el-upload>

    handleExceed(files, fileList) {
      this.$set(fileList[0], "raw", files[0]);
      this.$set(fileList[0], "name", files[0].name);
      this.$refs["rebateUpload"].clearFiles(); //清除文件
      this.$refs["rebateUpload"].handleStart(files[0]); //选择文件后的赋值方法
    },
    changeImg(res, file) {
      this.logo = file[0].url;
    },