Bumping gaia.json for 1 gaia revision(s) a=gaia-bump

========

https://hg.mozilla.org/integration/gaia-2_0/rev/51ef5f978669
Author: Gabriele Svelto <gsvelto@mozilla.com>
Desc: Bug 1019783 - Always display IMEI codes for all SIM slots r=Rik

(cherry picked from commit c329a67bafe60032820ab64b52c07c22eeff114e)
Bumping manifests a=b2g-bump