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

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https://hg.mozilla.org/integration/gaia-central/rev/671132cc327c
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #17547 from KevinGrandon/bug_971497_system2_home_gesture_2

Bug 971497 - [System2] Instantiable HomeGesture r=alive

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https://hg.mozilla.org/integration/gaia-central/rev/aac6a3be42a1
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Bug 971497 - [System2] Instantiable HomeGesture r=alive
Bumping manifests a=b2g-bump