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

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https://hg.mozilla.org/integration/gaia-central/rev/4b075d3d4d4a
Author: James Burke <jrburke@gmail.com>
Desc: Merge pull request #20813 from jrburke/bug1028055-email-reader-title

Bug 1028055 - Sender's email is not displayed In the details page of a received email r=mcav

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https://hg.mozilla.org/integration/gaia-central/rev/45ce016d4805
Author: jrburke <jrburke@gmail.com>
Desc: Bug 1028055 - Sender's email is not displayed In the details page of a received email
Bumping manifests a=b2g-bump