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

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https://hg.mozilla.org/integration/gaia-central/rev/6ef94e486227
Author: John Hu <johu@mozilla.com>
Desc: Merge pull request #15689 from russnicoletti/bug833438

Bug 833438 - Viewing video through activity doesn't pause after headset ..., r=johnhu

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https://hg.mozilla.org/integration/gaia-central/rev/d157a76112cb
Author: Russ Nicoletti <rnicoletti@mozilla.com>
Desc: Bug 833438 - Viewing video through activity doesn't pause after headset is removed

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "2bd430740c37b61b3eb1e64d1c6e041a969206d6", 
+    "revision": "6ef94e4862272fc32d13a7da65a514761bbe2c38", 
     "repo_path": "/integration/gaia-central"
 }