Bumping gaia.json for 3 gaia-central revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/6164cd3fe618
Author: Sergey Tupchiy <tupchii.sergii@gmail.com>
Desc: Bug 934402 - Write an atom to send SMS using 'MozSMS' API. r=zcampbell, r=fstrugariu, r=dhunt

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https://hg.mozilla.org/integration/gaia-central/rev/2acc9c726f72
Author: Ben Kelly <bkelly@mozilla.com>
Desc: Merge pull request #13602 from wanderview/contacts-monitor-no-timer-1

Bug 936908: Do not batch work from monitor onscreen/offscreen.  r=arcturus

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https://hg.mozilla.org/integration/gaia-central/rev/ddca309cf2f0
Author: Ben Kelly <ben@wanderview.com>
Desc: Bug 936908: Do not batch work from monitor onscreen/offscreen.

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "61e8c0a15b565bb5bc52ace32f094c875f614905", 
+    "revision": "6164cd3fe618cf527cc0dac89d385ca5e179640c", 
     "repo_path": "/integration/gaia-central"
 }