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