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

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https://hg.mozilla.org/integration/gaia-central/rev/a2d248a2e3d7
Author: Carsten Book <tomcat@mozilla.com>
Desc: Merge pull request #25797 from mancas/bug1091483_v2.2

Bug 1091483 - Unable to show stk dialog (e.g. user confirmation dialog). r=alive

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https://hg.mozilla.org/integration/gaia-central/rev/28bf9a7dc7fa
Author: Manuel Casas Barrado <manuel.casasbarrado@telefonica.com>
Desc: Bug 1091483 - Unable to show stk dialog (e.g. user confirmation dialog) when foreground app is Callscreen. Patch v2.2. r=alive
Bumping manifests a=b2g-bump