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

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https://hg.mozilla.org/integration/gaia-central/rev/f88be8e2bdfe
Author: Etienne Segonzac <etienne@segonzac.info>
Desc: Merge pull request #14660 from etiennesegonzac/bug-949487-window-manager-insta-kill

Bug 949487 -  Harden the AppWindowManager against apps that gets insta-killed r=alive

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https://hg.mozilla.org/integration/gaia-central/rev/cabdfa599bb7
Author: Etienne Segonzac <etienne@segonzac.info>
Desc: Bug 949487 -  Harden the AppWindowManager against app that gets
insta-killed