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

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https://hg.mozilla.org/integration/gaia-central/rev/4574b4be7f14
Author: vingtetun <21@vingtetun.org>
Desc: Merge pull request #12829 from vingtetun/utility_tray_event_fluffing

Bug 902393 - [Utility tray] Once the utility tray is pulled down it is n...

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https://hg.mozilla.org/integration/gaia-central/rev/589495f1ca66
Author: Vivien Nicolas <21@vingtetun.org>
Desc: Bug 902393 - [Utility tray] Once the utility tray is pulled down it is not possible to pull it back up. r=alive

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https://hg.mozilla.org/integration/gaia-central/rev/a4e0f440d4be
Author: vingtetun <21@vingtetun.org>
Desc: Merge pull request #12826 from vingtetun/settings.no.peek

Bug 920623 - Remove the css animation 'peek' hack in settings. r=kaze

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https://hg.mozilla.org/integration/gaia-central/rev/d1320d99c6c9
Author: Vivien Nicolas <21@vingtetun.org>
Desc: Bug 920623 - Remove the css animation 'peek' hack in settings. r=kaze

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "4a8dcbcad9433e7cb0b619d80b041219e5946130", 
+    "revision": "4574b4be7f14d41cc5a1bf9ca6b754bd8b35ba8e", 
     "repo_path": "/integration/gaia-central"
 }