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

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https://hg.mozilla.org/integration/gaia-central/rev/78ad2c5d6d67
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #15087 from eeejay/bug-957252

Bug 957252 - Update Screen Reader Simulator URL. r=kgrandon

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https://hg.mozilla.org/integration/gaia-central/rev/41ba0a639993
Author: Eitan Isaacson <eitan@monotonous.org>
Desc: Bug 957252 - Update Screen Reader Simulator URL.