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

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https://hg.mozilla.org/integration/gaia-central/rev/874cb7690678
Author: Ryan VanderMeulen <rvandermeulen@mozilla.com>
Desc: Merge pull request #19246 from azasypkin/bug-980461-date-format-note

Bug 980461 - [MMS] Visual adjustments to attachment download indicator. Added localization note for the expiry-date-format string. r=julien

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https://hg.mozilla.org/integration/gaia-central/rev/ab712609bdda
Author: Aleh Zasypkin <azasypkin@mozilla.com>
Desc: Bug 980461 - [MMS] Visual adjustments to attachment download indicator. Added localization note for the expiry-date-format string. r=julien
Bumping manifests a=b2g-bump