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

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https://hg.mozilla.org/integration/gaia-central/rev/7c86ea51249f
Author: John Ford <john@johnford.info>
Desc: Merge pull request #12111 from PinZhang/bug912317_add_speaker

Bug 912317: Add speaker switcher

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https://hg.mozilla.org/integration/gaia-central/rev/165c032e0c47
Author: pzhang <pzhang@mozilla.com>
Desc: Bug 912317: Add speaker switcher

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "63d432c3395f95c0ba19578487b796c1707042bd", 
+    "revision": "7c86ea51249f3cbcf9806bed104a283959035b13", 
     "repo_path": "/integration/gaia-central"
 }