Using gulp exec to run bash script - bash

Question

I am trying to use gulp exec to run a bash script with gulp that updates assets in the project. The directory of the script is as follows:
./assets/update_assets.sh
I have followed the documentation and my gulpfile look as follows:
'use-strict';
var gulp = require('gulp'),
gutil = require('gulp-util');
exec = require('child_process').exec;
gulp.task('update-assets', function (cb) {
exec('./assets/update_assets.sh', function(err, stdout, stderr) {
console.log(stdout);
console.log(stderr);
cb(err);
});
});
gulp.task('default', ['update-assets'], function() {
gulp.start('update-assets');
});
When I try and run gulp i get errors:
[15:13:47] Error: Command failed: /bin/sh -c ./assets/update_assets.sh
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 168 100 168 0 0 197 0 --:--:-- --:--:-- --:--:-- 197
tar: Unrecognized archive format
tar: Error exit delayed from previous errors.
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 168 100 168 0 0 288 0 --:--:-- --:--:-- --:--:-- 288
tar: could not chdir to 'README.md/'
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 168 100 168 0 0 265 0 --:--:-- --:--:-- --:--:-- 264
tar: Unrecognized archive format
tar: Error exit delayed from previous errors.
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 168 100 168 0 0 276 0 --:--:-- --:--:-- --:--:-- 276
tar: could not chdir to 'gulpfile.js/'
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 168 100 168 0 0 283 0 --:--:-- --:--:-- --:--:-- 282
tar: Unrecognized archive format
tar: Error exit delayed from previous errors.
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 168 100 168 0 0 268 0 --:--:-- --:--:-- --:--:-- 268
tar: could not chdir to 'package.json/'
at ChildProcess.exithandler (child_process.js:744:12)
at ChildProcess.emit (events.js:110:17)
at maybeClose (child_process.js:1008:16)
at Socket.<anonymous> (child_process.js:1176:11)
at Socket.emit (events.js:107:17)
at Pipe.close (net.js:476:12)