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

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https://hg.mozilla.org/integration/gaia-central/rev/73854709d1c7
Author: gitmai <mri@tid.es>
Desc: Merge pull request #14501 from gitmai/bug-944718-Broken-usage-widget

Bug 944718 - [Cost Control] Broken access to usage widget from utility t...
r=salva

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https://hg.mozilla.org/integration/gaia-central/rev/e862da538916
Author: mai <mri@tid.es>
Desc: Bug 944718 - [Cost Control] Broken access to usage widget from utility tray