coco.py uses non-existent method os.execute

[ssnl]

The method doesn't exist in python 2.7, 3.5, or 3.6.

[Cadene]

It should be os.system.

Thanks for reporting this issue.

[ssnl]

Do you mind if I submit a PR to fix those?

[Cadene]

Please do so.

Thank you!

[Cadene]

Fixed: #23