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

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https://hg.mozilla.org/integration/gaia-central/rev/781a4d935f32
Author: vingtetun <21@vingtetun.org>
Desc: Merge pull request #14397 from vingtetun/bug938312

Bug 938312 - Wrong orientation when starting browser in landscape mode. ...

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https://hg.mozilla.org/integration/gaia-central/rev/c92773dd9adb
Author: Vivien Nicolas <21@vingtetun.org>
Desc: Bug 938312 - Wrong orientation when starting browser in landscape mode. r=alive