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

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https://hg.mozilla.org/integration/gaia-central/rev/a8df0c02a4d8
Author: Jose M. Cantera <jmcanterafonseca@gmail.com>
Desc: Merge pull request #17160 from jmcanterafonseca/fix_fb_unfriend

Bug 981159 - [B2G][Contacts] Unfriend Facebook friends are not removed f...

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https://hg.mozilla.org/integration/gaia-central/rev/18dd3091241e
Author: Jose M. Cantera <jmcanterafonseca@gmail.com>
Desc: Bug 981159 - [B2G][Contacts] Unfriend Facebook friends are not removed from the user's contacts after import
Bumping manifests a=b2g-bump