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

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https://hg.mozilla.org/integration/gaia-central/rev/c19506403f71
Author: Ryan VanderMeulen <rvandermeulen@mozilla.com>
Desc: Merge pull request #18062 from arky/master

Bug 993095  - Add Tamil (ta)

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https://hg.mozilla.org/integration/gaia-central/rev/55059b49460a
Author: Arky <hitmanarky@gmail.com>
Desc: Bug 993095  - Add Tamil (ta)
Bumping manifests a=b2g-bump