Bumping gaia.json for 3 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/f55d747adb89
Author: Anthony Ricaud <anthony@ricaud.me>
Desc: Merge pull request #15874 from Rik/simslot-965155

Bug 965155 - SIM manager will set all outgoing settings to SIM 2 after r... r=etienne

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https://hg.mozilla.org/integration/gaia-central/rev/c2c20676697a
Author: Anthony Ricaud <anthony@ricaud.me>
Desc: Bug 965155 - SIM manager will set all outgoing settings to SIM 2 after reboot device

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https://hg.mozilla.org/integration/gaia-central/rev/b211f17e2d45
Author: Rick Waldron <waldron.rick@gmail.com>
Desc: Revert "Bug 959696 - [Messages][Drafts][Refactoring] Move draft saving on visibility change to ThreadUI, and only store drafts if new one is saved r=rwaldron"

This reverts commit 6c9fac83b743711d02c4a32e45cd145d8a85f7eb.
Bumping manifests a=b2g-bump