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

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https://hg.mozilla.org/integration/gaia-central/rev/acf0d1dfd548
Author: Yoshi Huang <allstars.chh@mozilla.com>
Desc: Merge pull request #18604 from svic/Bug-998111

Bug 998111 - Fix race condition while starting and stopping tilted UI. r=gweng

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https://hg.mozilla.org/integration/gaia-central/rev/24484423aaf2
Author: Siddartha Pothapragada <Siddartha.Pothapragada@telekom.com>
Desc: Bug 998111 - Fix race condition while starting and stopping tilted UI. r=gweng

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https://hg.mozilla.org/integration/gaia-central/rev/dadc6b723171
Author: Timothy Guan-tin Chien <timdream@gmail.com>
Desc: Merge pull request #18664 from timdream/keyboard-settings

Bug 988782 - Allow keyboard settings page manages it's own life, r=rudyl

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https://hg.mozilla.org/integration/gaia-central/rev/2e0b69366ab8
Author: Timothy Guan-tin Chien <timdream@gmail.com>
Desc: Bug 988782 - Allow keyboard settings page manages it's own life
Bumping manifests a=b2g-bump