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

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https://hg.mozilla.org/integration/gaia-central/rev/6991d4067741
Author: vingtetun <21@vingtetun.org>
Desc: Merge pull request #11344 from fcampo/TutorialSwipeLeft

Bug 901041 - Remove 'swipe left' screen in tutorial (as part of the first run experience)

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https://hg.mozilla.org/integration/gaia-central/rev/03ec92421539
Author: Fernando Campo <fernando.campo@o2.com>
Desc: Bug 901041 - Remove 'swipe left' screen in tutorial (as part of the first run experience)

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "c4acbffef44e649f328f9b9320defdc326209e50", 
+    "revision": "6991d4067741e0eb1eff1bafef7de820c8959cb2", 
     "repo_path": "/integration/gaia-central"
 }