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

========

https://hg.mozilla.org/integration/gaia-central/rev/218c8b6ad922
Author: vingtetun <21@vingtetun.org>
Desc: Merge pull request #12986 from brendandahl/pdfjs-0.8.629

Bug 929059 - Update pdf.js to version 0.8.629.

========

https://hg.mozilla.org/integration/gaia-central/rev/db54b13503ad
Author: Brendan Dahl <brendan.dahl@gmail.com>
Desc: Bug 929059 - Update pdf.js to version 0.8.629.