Bumping gaia.json for 2 gaia-central revision(s) a=gaia-bump

========

https://hg.mozilla.org/integration/gaia-central/rev/6fbc3880dac7
Author: Trif Andrei-Alin <trifandreialin@gmail.com>
Desc: Merge pull request #13474 from teodosia/sms-contact-travis

Bug 935587 - test_sms_add_contact.py - Adjust assertion and enable test for Travis

========

https://hg.mozilla.org/integration/gaia-central/rev/57238f6bfbe1
Author: Teodosia Pop <teodosia.pop@gmail.com>
Desc: Bug 935587 - test_sms_add_contact.py - Adjust assertion and enable test for Travis