put(serialized, path = this.path, o = {}) {
      return this.request("https://content.dropboxapi.com/2/files/upload", serialized, "POST", {
        headers: {
          "Dropbox-API-Arg": JSON.stringify({
            path,
            mode: "overwrite"
          }),
          "Content-Type": "application/octet-stream"
        }
      });
    }
Saves a file to the backend.
@param {Object} file - An object with name & data keys
@return {Promise} A promise that resolves when the file is saved.