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

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https://hg.mozilla.org/integration/gaia-central/rev/6cd910214dae
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #17006 from KevinGrandon/bug_971553_system2_software_button_manager

Bug 971553 - [System2] Instantiable SoftwareButtonManager r=alive

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https://hg.mozilla.org/integration/gaia-central/rev/fef3ae06f077
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Bug 971553 - [System2] Instantiable SoftwareButtonManager r=alive
Bumping manifests a=b2g-bump