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

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https://hg.mozilla.org/integration/gaia-central/rev/2c8ad9bb0ecf
Author: Fabien Cazenave <fabien@cazenave.cc>
Desc: Merge pull request #14751 from TheoChevalier/call-waiting-switch-fix

Bug 951123 - [Settings] Call waiting switch on "Confirm Call waiting", r=kaze

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https://hg.mozilla.org/integration/gaia-central/rev/6fb9727f76f0
Author: TheoChevalier <theo.chevalier11@gmail.com>
Desc: Bug 951123 - [Settings] Call waiting switch on "Confirm Call waiting" screen is broken

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "1485522e12985eb8a2fc7de6c33f0ae705ee587e", 
+    "revision": "2c8ad9bb0ecf5184c950c8b94793c55d47962b5c", 
     "repo_path": "/integration/gaia-central"
 }