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

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https://hg.mozilla.org/integration/gaia-central/rev/1a6d1000f29f
Author: James Burke <jrburke@gmail.com>
Desc: Merge pull request #23230 from jrburke/bug1005446-email-custom-elements

Bug 1005446 - [email] try custom elements for cards r=asuth

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https://hg.mozilla.org/integration/gaia-central/rev/a402cf384c06
Author: jrburke <jrburke@gmail.com>
Desc: Bug 1005446 - [email] custom elements for cards
avoid body work if the header no longer matches, or if card has been destroyed
Bumping manifests a=b2g-bump