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

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https://hg.mozilla.org/integration/gaia-central/rev/75e74c6b57d4
Author: Timothy Guan-tin Chien <timdream@gmail.com>
Desc: Merge pull request #15031 from timdream/keyboard-launch-on-boot

Bug 956269 - Introduce a setting key to disable launching a keyboard app in background during boot, r=gary

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https://hg.mozilla.org/integration/gaia-central/rev/e3eb7fc9540c
Author: Timothy Guan-tin Chien <timdream@gmail.com>
Desc: Bug 956269 - Introduce a setting key to disable launching a keyboard app in background during boot