Bumping gaia.json for 4 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/14be4007babb
Author: Fabrice Desré <fabrice@desre.org>
Desc: Merge pull request #17034 from vvuk/tiling

Add default tiles pref settings to Gaia

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https://hg.mozilla.org/integration/gaia-central/rev/e7874fb2468a
Author: Vladimir Vukicevic <vladimir@pobox.com>
Desc: b=981733, Add more tiles prefs to Gaia, and have default settings in common-settings.json, r=21

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https://hg.mozilla.org/integration/gaia-central/rev/a5513c842e8c
Author: Jan Keromnes <janx@linux.com>
Desc: Merge pull request #17036 from jankeromnes/appwindow

Bug 980332 - Infinite loop in apps/system/js/devtools_view.js. r=janx

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https://hg.mozilla.org/integration/gaia-central/rev/9aeb5497db4d
Author: Vivien Nicolas <21@vingtetun.org>
Desc: Bug 980332 - Infinite loop in apps/system/js/devtools_view.js. r=janx
Bumping manifests a=b2g-bump