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

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https://hg.mozilla.org/integration/gaia-central/rev/afb2469db615
Author: James Burke <jrburke@gmail.com>
Desc: Merge pull request #15430 from jrburke/bug960343-email-minify

Bug 960343 - email: minify JS r=asuth

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https://hg.mozilla.org/integration/gaia-central/rev/60b9d666d9cc
Author: jrburke <jrburke@gmail.com>
Desc: Bug 960343 - email: minify JS
Bumping manifests a=b2g-bump