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

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https://hg.mozilla.org/integration/gaia-central/rev/5262006180e3
Author: Etienne Segonzac <etienne@segonzac.info>
Desc: Merge pull request #18888 from etiennesegonzac/bug-1002459-hold-l10n

Bug 1002459 - Fixing an l10n issue with the hold button. r=ferjm

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https://hg.mozilla.org/integration/gaia-central/rev/b471d97fd7e1
Author: Etienne Segonzac <etienne@segonzac.info>
Desc: Bug 1002459 - Fixing an l10n issue with the hold button.
/!\ No change to the main en-US file.
Bumping manifests a=b2g-bump
Merge b-i to m-c