Bumping gaia.json for 4 gaia-central revision(s)

========

https://hg.mozilla.org/integration/gaia-central/rev/e7b4b6ba9e27
Author: Fabien Cazenave <fabien@cazenave.cc>
Desc: Merge pull request #12158 from lissyx/bug914599

Bug 914599 - Improve Call Settings when FDN is enabled, r=kaze

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https://hg.mozilla.org/integration/gaia-central/rev/390ffaf03cf6
Author: Alexandre Lissy <lissyx+github@lissyx.dyndns.org>
Desc: Bug 914599 - Improve Call Settings when FDN is enabled

When the Fixed Dialing Numbers options is enabled, many features are
disabled, and USSD/MMI codes fall into this set. This will thus make the
many call settings parameters getting into error state. The present
commit aims at: avoiding undefined state of the call settings, and
improving the feedback we send to user by clearly stating that call
forwaring options are unavaiable due to FDN enabled.

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https://hg.mozilla.org/integration/gaia-central/rev/485adbe8484f
Author: Olav Nymoen <olav@comoyo.com>
Desc: Merge pull request #12172 from comoyo/oop_fix

Bug 915684: Fix for url var not in scope after refactor. r=alive

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https://hg.mozilla.org/integration/gaia-central/rev/3a41c96dcc5a
Author: Olav Nymoen <olav@comoyo.com>
Desc: Bug 915684: Fix for url var not in scope after refactor. r=alive

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "67e06d07f4c5efd6df87e25a017817d5c28e4f8e", 
+    "revision": "e7b4b6ba9e2786df88be8755e2e97702bed193b2", 
     "repo_path": "/integration/gaia-central"
 }