Bumping gaia.json for 4 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/7ede04be6dcb
Author: Ryan VanderMeulen <rvandermeulen@mozilla.com>
Desc: Merge pull request #20909 from anefzaoui/bug-1029175

Bug 1029175 - [Homescreen] Notification tray needs visual attention

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https://hg.mozilla.org/integration/gaia-central/rev/6c8774ddb9b4
Author: Ahmed Nefzaoui <nefzaoui.ahmed@hotmail.com>
Desc: Bug 1029175 - [Homescreen] Notification tray needs visual attention

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https://hg.mozilla.org/integration/gaia-central/rev/06f9935af929
Author: Ryan VanderMeulen <rvandermeulen@mozilla.com>
Desc: Merge pull request #21423 from TheoChevalier/bug-1028808-inconsistency-homescreen

Bug 1028808 - Inconsistent spelling of "Homescreen" across Gaia apps

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https://hg.mozilla.org/integration/gaia-central/rev/3f1b9502e193
Author: TheoChevalier <theo.chevalier11@gmail.com>
Desc: Bug 1028808 - Inconsistent spelling of "Homescreen" across Gaia apps
Bumping manifests a=b2g-bump