Bumping gaia.json for 3 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/c041fbb3644d
Author: Michael Henretty <michael.henretty@gmail.com>
Desc: Merge pull request #19177 from mikehenrty/bug-968483-rnowm

Bug 968483 rnowm

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https://hg.mozilla.org/integration/gaia-central/rev/2ae6e9b6cae9
Author: Michael Henretty <michael.henretty@gmail.com>
Desc: Bug 968483 - Fixes to increaded back button size, python tests

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https://hg.mozilla.org/integration/gaia-central/rev/4cbdf6405a47
Author: rnowm <arnau@arnaumarch.com>
Desc: Bug 968483 - [Building Blocks] Update header design to accommodate larger back-button
Bumping manifests a=b2g-bump