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

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https://hg.mozilla.org/integration/gaia-central/rev/b2db3a261819
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #23693 from KevinGrandon/bug_967516_part_1_screen_timeout

Bug 967516 - Part 1 - Decouple screen timeout from device debug config

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https://hg.mozilla.org/integration/gaia-central/rev/42c4dcf84200
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Bug 967516 - Part 1 - Decouple screen timeout from device debug config r=ochameau
Bumping manifests a=b2g-bump