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

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https://hg.mozilla.org/integration/gaia-central/rev/f978663e75bc
Author: Marcus Cavanaugh <m@mcav.com>
Desc: Merge pull request #23232 from mcav/emailjs

Bug 885110 - Switch to email.js libraries. r=asuth r=jrburke r=mcav

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https://hg.mozilla.org/integration/gaia-central/rev/4c49978bc6b1
Author: Marcus Cavanaugh <m@mcav.com>
Desc: Bug 885110 - [email] Switch to email.js libraries. r=asuth r=jrburke r=mcav
Bumping manifests a=b2g-bump