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

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https://hg.mozilla.org/integration/gaia-central/rev/39f8b51560ab
Author: Aleh Zasypkin <aleh.zasypkin@gmail.com>
Desc: Merge pull request #21997 from azasypkin/bug-1041124-messages-manager-events

Bug 1041124 - [Messages][Refactoring] Make use of EventDispatcher in MessageManager. r=julien

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https://hg.mozilla.org/integration/gaia-central/rev/46ed5ddb4704
Author: Aleh Zasypkin <azasypkin@mozilla.com>
Desc: Bug 1041124 - [Messages][Refactoring] Make use of EventDispatcher in MessageManager. r=julien

b2g/config/gaia.json

@@ -4,6 +4,6 @@
         "remote": "", 
         "branch": ""
     }, 
-    "revision": "a5e18021bfd43c764a2a28a49c6a14f1c057aba8", 
+    "revision": "39f8b51560ab77b7333e8d6340697df19a5fa58a", 
     "repo_path": "/integration/gaia-central"
 }