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

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https://hg.mozilla.org/integration/gaia-central/rev/d2cd15f3a4be
Author: Pavel Ivanov <pivanov@mozilla.com>
Desc: Merge pull request #13783 from pivanov/bug-939147

Bug 939147 - [Action Icons - Browser] Remove shadows from action icons

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https://hg.mozilla.org/integration/gaia-central/rev/8192ab2b1c43
Author: Pavel Ivanov <pivanov@mozilla.com>
Desc: Bug 939147 - Remove shadows from browser action icons

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "62ffee1a7ebd3be475695decb86912b254144e39", 
+    "revision": "d2cd15f3a4beb391b92a873b58421e01e163fe4a", 
     "repo_path": "/integration/gaia-central"
 }