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

========

https://hg.mozilla.org/integration/gaia-central/rev/644d444e2368
Author: Francisco Jordano <arcturus@ardeenelinfierno.com>
Desc: Merge pull request #13027 from jmcanterafonseca/fix_mozContact_merge

Bug 929914 - Revise contacts merging with respect to mozContact construc...

========

https://hg.mozilla.org/integration/gaia-central/rev/78ee62c38fb2
Author: Jose M. Cantera <jmcanterafonseca@gmail.com>
Desc: Bug 929914 - Revise contacts merging with respect to mozContact constructor