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

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https://hg.mozilla.org/integration/gaia-central/rev/79e5f0291397
Author: Arnau <arnau@arnaumarch.com>
Desc: Merge pull request #19773 from rnowm/1017509

Bug 1017509 - [Download Manager] Deselect all button is not displayed successfully r=francisco

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https://hg.mozilla.org/integration/gaia-central/rev/755ec42715fb
Author: rnowm <arnau@arnaumarch.com>
Desc: Bug 1017509 - [Download Manager] Deselect all button is not displayed successfully
Bumping manifests a=b2g-bump