Bumping gaia.json for 3 gaia-central revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/facd96e4c918
Author: Zac Campbell <zcampbell@mozilla.com>
Desc: Bug 942809 - Unxfail test_settings_airplane_mode.py a=testonly r=me

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https://hg.mozilla.org/integration/gaia-central/rev/52f31d36fea8
Author: Arnau <arnau@arnaumarch.com>
Desc: Merge pull request #13951 from rnowm/940984

Bug 940984 - [BB] Change button padding in action menu building block

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https://hg.mozilla.org/integration/gaia-central/rev/63231f3406d0
Author: rnowm <arnau@arnaumarch.com>
Desc: Bug 940984 - [BB] Change button padding in action menu building block