function openDocument(path:string, scheme:string) {
  if(Platform.OS === 'ios')
    return RNFetchBlob.openDocument('file://' + path, scheme)
  else
    return Promise.reject('RNFetchBlob.previewDocument only supports IOS.')
}
Preview a file using UIDocumentInteractionController
@param  {string]} path Path of the file to be open.
@param  {string} scheme URI scheme that needs to support, optional
@return {Promise}