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

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https://hg.mozilla.org/integration/gaia-central/rev/bba6a25c9308
Author: Joan Leon <joan.leon@gmail.com>
Desc: Merge pull request #16657 from nucliweb/976665-Cost-Control

Add display:flex for fix height 100% on iframe

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https://hg.mozilla.org/integration/gaia-central/rev/878660c8c91c
Author: Joan Leon <joan.leon@gmail.com>
Desc: Add display:flex for fix height 100% on iframe
Bumping manifests a=b2g-bump