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

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https://hg.mozilla.org/integration/gaia-central/rev/2712836efbca
Author: Carsten Book <tomcat@mozilla.com>
Desc: Merge pull request #19597 from kamituel/Bug_1015084_throw_errors

Bug 1015084 - unit tests and fixes for NfcBuffer. r=alive

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https://hg.mozilla.org/integration/gaia-central/rev/ff61c1c16dd3
Author: Kamil Leszczuk <kamituel@gmail.com>
Desc: Bug 1015084: unit tests and fixes for NfcBuffer
Bumping manifests a=b2g-bump