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

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https://hg.mozilla.org/integration/gaia-central/rev/63864e9e18de
Author: George <georgeiscoming@gmail.com>
Desc: Merge pull request #12876 from cctuan/911117

Bug 911117 - [flatfish] Headset icon is lost on status bar if booting up...

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https://hg.mozilla.org/integration/gaia-central/rev/2536391e0165
Author: cctuan <georgeiscoming@gmail.com>
Desc: Bug 911117 - [flatfish] Headset icon is lost on status bar if booting up with headset plugged

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "51ea613dbd116b4676a2b89733c38c7487adfedb", 
+    "revision": "63864e9e18de5d4c254c366bb6ca4738c19921c3", 
     "repo_path": "/integration/gaia-central"
 }