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

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https://hg.mozilla.org/integration/gaia-central/rev/6c712d2d7297
Author: James Lal <james@lightsofapollo.com>
Desc: Merge pull request #11731 from lightsofapollo/test-calendars

Test calendars

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https://hg.mozilla.org/integration/gaia-central/rev/b4b9d97dd735
Author: James Lal <james@lightsofapollo.com>
Desc: Bug 908943 - remove client.helper.wait in calendar

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "1353a60aea42027e87d446d303b7f1298db8bc4a", 
+    "revision": "6c712d2d7297116c4bb540451bf5d38f8ff19622", 
     "repo_path": "/integration/gaia-central"
 }