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

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https://hg.mozilla.org/integration/gaia-central/rev/1b8b899e99f7
Author: Yura Zenevich <yura.zenevich@gmail.com>
Desc: Merge pull request #22593 from yzen/bug-1030431

Bug 1030431 - correctly handling dialog overlay visibility in the dialer...

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https://hg.mozilla.org/integration/gaia-central/rev/b911cda448ae
Author: Yura Zenevich <yzenevich@mozilla.com>
Desc: Bug 1030431 - correctly handling dialog overlay visibility in the dialer and callscreen apps.
Bumping manifests a=b2g-bump