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

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https://hg.mozilla.org/integration/gaia-central/rev/5101679e2445
Author: Arnau <arnau@arnaumarch.com>
Desc: Merge pull request #17971 from rnowm/992121

Bug 992121 - [Settings] not showing correct spinner r=pivanov

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https://hg.mozilla.org/integration/gaia-central/rev/18b2ece56635
Author: rnowm <arnau@arnaumarch.com>
Desc: Bug 992121 - [Settings] not showing correct spinner
Bumping manifests a=b2g-bump