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

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https://hg.mozilla.org/integration/gaia-central/rev/407020347f28
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #20637 from KevinGrandon/bug_1026759_gaia_grid_dereference

Bug 1026759 - [GaiaGrid] Re-using grid item objects causes them to not render

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https://hg.mozilla.org/integration/gaia-central/rev/d681213ecb3c
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Bug 1026759 - [GaiaGrid] Re-using grid item objects causes them to not render r=amirn

b2g/config/gaia.json

@@ -4,6 +4,6 @@
         "remote": "", 
         "branch": ""
     }, 
-    "revision": "75365f3376daac9954e812f4d1f610823778d897", 
+    "revision": "407020347f28d282d0b91ef7669607db5d58f4a7", 
     "repo_path": "/integration/gaia-central"
 }