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

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https://hg.mozilla.org/integration/gaia-central/rev/fdf0c264f9ec
Author: lissyx <lissyx+github@lissyx.dyndns.org>
Desc: Merge pull request #14535 from lissyx/bug948429

Bug 948429 - Documenting the usage of Xvfb and keep tests quiet r=gaye

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https://hg.mozilla.org/integration/gaia-central/rev/59a7b7e4abaa
Author: Alexandre Lissy <lissyx+github@lissyx.dyndns.org>
Desc: Bug 948429 - Documenting the usage of Xvfb and keep tests quiet