Bumping gaia.json for 4 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/914e08f20e7a
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #16225 from KevinGrandon/bug_971450_activities_v2

Bug 971450 - [System2] Instantiable Activities r=alive

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https://hg.mozilla.org/integration/gaia-central/rev/bd6002731147
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Bug 971450 - [System2] Instantiable Activities r=alive

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https://hg.mozilla.org/integration/gaia-central/rev/0f09db9c31c9
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #16220 from KevinGrandon/bug_971483_devtools_layer_v2

Bug 971483 - [System2] Instantiable DevToolsLayer r=alive

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https://hg.mozilla.org/integration/gaia-central/rev/29974a9a2a50
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Bug 971483 - [System2] Instantiable DevToolsLayer r=alive
Bumping manifests a=b2g-bump