Elemennt文件上传el-upload设置上传文件图片格式限制

<el-col :span="22">
            <el-form-item label="图片" prop="pic"
                :rules="[
                  { min: 0, message: ‘最小长度是0个字‘, trigger: ‘blur‘ }
                 ]">
              <el-upload ref="pic"
              v-if="visible"
              accept=".jpg,.jpeg,.png,.gif,.bmp,.pdf,.JPG,.JPEG,.PBG,.GIF,.BMP,.PDF"
              list-type="picture-card"