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

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https://hg.mozilla.org/integration/gaia-central/rev/8539eb2c32f0
Author: Ryan VanderMeulen <rvandermeulen@mozilla.com>
Desc: Merge pull request #12426 from GeorgiaWang/Bug919969

Bug 919969 - Add illegal sim state support in Settings

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https://hg.mozilla.org/integration/gaia-central/rev/22406a06f44c
Author: Georgia Wang <gwang@mozilla.com>
Desc: Bug 919969 - Add illegal sim state support in Settings

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "c58a78c93c48bf87c72d77497e63f13680be9cb8", 
+    "revision": "8539eb2c32f06040d4dfbb663a3047a72e272dc9", 
     "repo_path": "/integration/gaia-central"
 }