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

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https://hg.mozilla.org/integration/gaia-central/rev/6ac60fe55430
Author: Zac <zcampbell@mozilla.com>
Desc: Merge pull request #20294 from chirarobert/tap_mp_icon

Bug 1023208 - [v2.0][v2.1] Fix test_marketplace_launch failure

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https://hg.mozilla.org/integration/gaia-central/rev/255cd65fd715
Author: chirarobert <robert.chira@softvision.ro>
Desc: Bug 1023208 - [v2.0][v2.1] Fix test_marketplace_launch failure
Bumping manifests a=b2g-bump