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

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https://hg.mozilla.org/integration/gaia-central/rev/5949a2dd24a0
Author: AndreiH <andrei.hutusoru@softvision.ro>
Desc: Merge pull request #18411 from zacc/bug_997633

Bug 997633 - Update Python marionette_client to 0.7.6

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https://hg.mozilla.org/integration/gaia-central/rev/34cff87cb2ca
Author: Zac <zcampbell@mozilla.com>
Desc: Bug 997633 - Update Python marionette_client to 0.7.6
Bumping manifests a=b2g-bump