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

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https://hg.mozilla.org/integration/gaia-central/rev/b5e6dc93ee51
Author: Jose M. Cantera <jmcanterafonseca@gmail.com>
Desc: Merge pull request #15548 from jmcanterafonseca/facebook_logout

Bug 956893 - [B2G][Contacts][Facebook] Unable to log out from Facebook i...

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https://hg.mozilla.org/integration/gaia-central/rev/6f84811540a1
Author: Jose M. Cantera <jmcanterafonseca@gmail.com>
Desc: Bug 956893 - [B2G][Contacts][Facebook] Unable to log out from Facebook in Contacts
Bumping manifests a=b2g-bump