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

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https://hg.mozilla.org/integration/gaia-central/rev/acba8a7d5451
Author: David Flanagan <dflanagan@mozilla.com>
Desc: Merge pull request #14473 from davidflanagan/bug945376

Bug 945376: correctly handle the None alert tone setting r=pdahiya

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https://hg.mozilla.org/integration/gaia-central/rev/e416cc78aeea
Author: David Flanagan <dflanagan@mozilla.com>
Desc: Bug 945376: correctly handle the None alert tone setting