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

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https://hg.mozilla.org/integration/gaia-central/rev/fd494cd83a65
Author: lissyx <lissyx+github@lissyx.dyndns.org>
Desc: Merge pull request #12847 from lissyx/bug913324

Bug 913324 - Select biggest icon that fits on the screen r=vingetun

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https://hg.mozilla.org/integration/gaia-central/rev/9e0d60a008bc
Author: Alexandre Lissy <lissyx+github@lissyx.dyndns.org>
Desc: Bug 913324 - Select biggest icon that fits on the screen

When launching an app, we display one of the icon defined in its
manifest. If the application defines several ones, then we need to
select the biggest one that fits into the screen.