axios 上传 blob

举个栗子，vue-cropper 返回的图片是 blob 格式，我通过 axios 上传的代码是这么写：

import axios from 'axios'

uploadAvatar() {
  return new Promise((resolve, reject) => {
    this.$refs.cropper.getCropBlob(data => {
      // console.log(data)
      let formData = new FormData()
      formData.append('file', data)
      axios({
        method: 'post',
        url: 'https://www.mocky.io/v2/5cc8019d300000980a055e76',
        data: formData,
        headers: {
          'Content-Type': 'multipart/form-data'
        }
      }).then(res => {
        resolve(res)
      }).catch(err => {
        reject(err)
      })
    })
  })
}