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

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https://hg.mozilla.org/integration/gaia-central/rev/8533045319a0
Author: Carsten Book <tomcat@mozilla.com>
Desc: Merge pull request #20810 from flodolo/bug1028250

Bug 1028250 - [contacts] Remove unused strings custom.placeholder. r=francisco

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https://hg.mozilla.org/integration/gaia-central/rev/14b45f78e008
Author: Francesco Lodolo (:flod) <flod@lodolo.net>
Desc: Bug 1028250 - [contacts] Remove unused strings custom.placeholder
Bumping manifests a=b2g-bump