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

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https://hg.mozilla.org/integration/gaia-central/rev/5b4a1d76f824
Author: Ryan VanderMeulen <rvandermeulen@mozilla.com>
Desc: Merge pull request #21550 from AdFad666/master

Bug 1036553 Fix cropped software home button

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https://hg.mozilla.org/integration/gaia-central/rev/c409e7af7e55
Author: Adam Farden <adam@farden.cz>
Desc: Bug 1036553 Fix cropped software home button
Bumping manifests a=b2g-bump