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

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https://hg.mozilla.org/integration/gaia-central/rev/bf89769ca347
Author: Jose M. Cantera <jmcanterafonseca@gmail.com>
Desc: Merge pull request #13554 from jmcanterafonseca/fix_fb_index

Bug 936373 - Optimize FB datastore index refresh by tracking revisionId ...

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https://hg.mozilla.org/integration/gaia-central/rev/baec6dcb6b96
Author: Jose M. Cantera <jmcanterafonseca@gmail.com>
Desc: Bug 936373 - Optimize FB datastore index refresh by tracking revisionId number

b2g/config/gaia.json

@@ -1,4 +1,4 @@
 {
-    "revision": "9073617f68b6cd1e413664a0375da9d1e526efee", 
+    "revision": "bf89769ca347c027a4dc1decbc42179bbbe26044", 
     "repo_path": "/integration/gaia-central"
 }