Bumping gaia.json for 2 gaia-central revision(s)

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https://hg.mozilla.org/integration/gaia-central/rev/20869b028aab
Author: Rex KM Lee <rexboy@mozilla.com>
Desc: Merge pull request #10855 from rexboy7/fixhd-881143-dialer-master

Bug 881143 - [HD][Dialer] hdpi/xhdpi resolution assets and layout for Dialer app. r=gtorodelvalle

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https://hg.mozilla.org/integration/gaia-central/rev/92424a531110
Author: Rex Lee <rexboy@mozilla.com>
Desc: Bug 881143 - [HD][Dialer] hdpi/xhdpi resolution assets and layout for Dialer app