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

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https://hg.mozilla.org/integration/gaia-central/rev/a02925eb225c
Author: Julien Wajsberg <felash@gmail.com>
Desc: Merge pull request #10590 from oconnore/879203-homescreen-opacity

Bug 879203 - opacity transition in home screen is not smooth r=crdlc

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https://hg.mozilla.org/integration/gaia-central/rev/76bac192d29d
Author: Eric O'Connor <eric@bocoup.com>
Desc: Move OPACITY_STEPS to the list of constants at the top of the file.
  Pull the step function out of the event handling function.
  Improve comments