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

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https://hg.mozilla.org/integration/gaia-central/rev/a9284b9920ee
Author: Carsten Book <tomcat@mozilla.com>
Desc: Merge pull request #25221 from kumarrishav/Bug-1082908

Bug 1082908 - Background color of contact list should be other than white so that it differ from empty space. r=felash

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https://hg.mozilla.org/integration/gaia-central/rev/a63240aa6fae
Author: kumarrishav <rishav006@gmail.com>
Desc: Bug 1082908 - Background color of contact list should be other than white so that it differ from empty space. r=julienw
Bumping manifests a=b2g-bump