Bumping gaia.json for 4 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/8b785d014387
Author: Timothy Guan-tin Chien <timdream@gmail.com>
Desc: Merge pull request #19775 from anvk/988697

Bug 988697: Adding a unit test for idletimer.js, r=timdream

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https://hg.mozilla.org/integration/gaia-central/rev/2cd26a2345dc
Author: Alexey Novak <alexey.novak.mail@gmail.com>
Desc: Bug 988697: Adding a unit test for idletimer.js, r=timdream

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https://hg.mozilla.org/integration/gaia-central/rev/fc8cc7cc1a6d
Author: Timothy Guan-tin Chien <timdream@gmail.com>
Desc: Merge pull request #20353 from timdream/input-switch-flash

Bug 1016283 - Prevent flash of black when switching layout of the same keyboard, r=rudyl

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https://hg.mozilla.org/integration/gaia-central/rev/711d2cc7ba50
Author: Timothy Guan-tin Chien <timdream@gmail.com>
Desc: Bug 1016283 - Prevent flash of black when switching layout of the same keyboard
Bumping manifests a=b2g-bump