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

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https://hg.mozilla.org/integration/gaia-central/rev/f8a45381d9b1
Author: Zac <zcampbell@mozilla.com>
Desc: Merge pull request #18832 from zacc/bug_1003853

Bug 1003853 - Use remembered is_desktop_b2g property rather than marione...

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https://hg.mozilla.org/integration/gaia-central/rev/170a13db0a8c
Author: Zac <zcampbell@mozilla.com>
Desc: Bug 1003853 - Add comment for marionette.instance and restart
Bumping manifests a=b2g-bump