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

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https://hg.mozilla.org/integration/gaia-central/rev/c55d4ca164d0
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #18846 from KevinGrandon/bug_971543_system2_instantiable_rocketbar

Bug 971543 - [System2] Make Rocketbar instantiable

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https://hg.mozilla.org/integration/gaia-central/rev/50c83e7e3821
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Bug 971543 - [System2] Make Rocketbar instantiable r=benfrancis
Bumping manifests a=b2g-bump