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

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https://hg.mozilla.org/integration/gaia-central/rev/39ec2452c51c
Author: Fernando Jiménez Moreno <ferjmoreno@gmail.com>
Desc: Merge pull request #16369 from ferjm/fxa-refresh-auth-2

Bug 968294 - Refresh authentication UI. r=alive

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https://hg.mozilla.org/integration/gaia-central/rev/beb29ab46bb4
Author: Fernando Jiménez <ferjmoreno@gmail.com>
Desc: Bug 968294 - Refresh authentication UI. r=alive
Bumping manifests a=b2g-bump