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

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https://hg.mozilla.org/integration/gaia-central/rev/760d7ac20f72
Author: Fernando Campo <fernando.campo@telefonica.com>
Desc: Merge pull request #20027 from fcampo/fb-notif-api-948447

Bug 948447 - Convert Facebook to new Notification API (r=jmcf)

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https://hg.mozilla.org/integration/gaia-central/rev/5d55f116490a
Author: Fernando Campo <fernando.campo@telefonica.com>
Desc: Bug 948447 - Convert Facebook to new Notification API
Bumping manifests a=b2g-bump