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

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https://hg.mozilla.org/integration/gaia-central/rev/fd425823b0bc
Author: David Flanagan <dflanagan@mozilla.com>
Desc: Merge pull request #14909 from davidflanagan/bug951932

Bug 951932: don't allow pick from Music for ringtones r=dmarcos

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https://hg.mozilla.org/integration/gaia-central/rev/dd976f9b6deb
Author: David Flanagan <dflanagan@mozilla.com>
Desc: Bug 951932: don't allow pick from Music for ringtones