Bumping gaia.json for 4 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/84a9a57e4571
Author: autolander <bug.autolander@gmail.com>
Desc: Bug 1156915 - merge pull request #29698 from punamdahiya:Bug1156915 to mozilla-b2g:master

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https://hg.mozilla.org/integration/gaia-central/rev/a486f59028b6
Author: Punam Dahiya <punamdahiya@yahoo.com>
Desc: Bug 1156915 - [Gallery][RTL][Image Edit] Exposure slider positive/negative signs should always show on left of numbers r=djf

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https://hg.mozilla.org/integration/gaia-central/rev/45967f36aa6a
Author: autolander <bug.autolander@gmail.com>
Desc: Bug 1113466 - merge pull request #29470 from steveck-chung:network-alerts-for-CDMA to mozilla-b2g:master

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https://hg.mozilla.org/integration/gaia-central/rev/075df147c76d
Author: Steve Chung <schung@mozilla.com>
Desc: Bug 1113466 - [Network Alert] Checking CDMA service category to classify CDMA CMAS correctly, r=julienw

b2g/config/gaia.json

@@ -1,9 +1,9 @@
 {
     "git": {
-        "git_revision": "27d008de10e77f30a1ab2413bdd0cf7f07c92001", 
+        "git_revision": "d981ebf30aca286ba8da53b8eb2f8eb21dfee406", 
         "remote": "https://git.mozilla.org/releases/gaia.git", 
         "branch": ""
     }, 
-    "revision": "b7fd002afc53b940e2bfa9329f0bc7e4d8c38234", 
+    "revision": "84a9a57e4571817b55a7047f8fc783da9479ebc8", 
     "repo_path": "integration/gaia-central"
 }