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

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https://hg.mozilla.org/integration/gaia-central/rev/cf31c17dffa0
Author: James Lal <james@lightsofapollo.com>
Desc: Merge pull request #13361 from bobsilverberg/xfail_clock_tbpl

Bug 932491 - Intermittent test_clock_set_alarm_snooze.py

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https://hg.mozilla.org/integration/gaia-central/rev/7b4835712f51
Author: Bob Silverberg <bob.silverberg@gmail.com>
Desc: Bug 932491 - Intermittent test_clock_set_alarm_snooze.py

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "fbe8db49928d667dda2af9ed1d6c5ecdfcce49b8", 
+    "revision": "cf31c17dffa07c11b9c8076488a0d7b6aa28a672", 
     "repo_path": "/integration/gaia-central"
 }