Update promisify.js

[krjj]

Description

Fix for unhandled exception getaddrinfo EAI_AGAIN when no internet connectivity is available.

Checklist

• [x ] Code compiles correctly
• [] Created tests which fail without the change (if possible)
• [] All tests passing
• [] Extended the README / documentation, if necessary
• [ ] Added myself / the copyright holder to the AUTHORS file

[lathropd]

breaks current tests