Bumping gaia.json for 1 gaia-central revision(s)

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https://hg.mozilla.org/integration/gaia-central/rev/f7f349019ccb
Author: Mike Pennisi <mike@mikepennisi.com>
Desc: Bug 883813 - [SMS][MMS] Placeholder string "Message" is not localizable r=julienw

Use HTML5 "data-" attribute for the localization value because setting
arbitrary elements is explicitly *not* supported by Gaia's L10n library.