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

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https://hg.mozilla.org/integration/gaia-central/rev/a815ebbbe084
Author: Jose M. Cantera <jmcanterafonseca@gmail.com>
Desc: Merge pull request #10974 from jmcanterafonseca/contacts_matcher_v1

Bug 889756 - Design and implement a ContactsMatcher module

========

https://hg.mozilla.org/integration/gaia-central/rev/763808ee9b75
Author: Jose M. Cantera <jmcanterafonseca@gmail.com>
Desc: Bug 889756 - Design and implement a ContactsMatcher module

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "7b11320c60264fc82adf668a3972f90e50de9c5a", 
+    "revision": "a815ebbbe084e5c278f65c73f183b89194e3833e", 
     "repo_path": "/integration/gaia-central"
 }