Bumping gaia.json for 1 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/7b386168c3f8
Author: jrburke <jrburke@gmail.com>
Desc: Revert "Merge pull request #15430 from jrburke/bug960343-email-minify"

This reverts commit e58e11c376048692a2c6830756e135f7c52f48a4, reversing
changes made to 8d18b1e2fd06c84a879f99f6e8ca1f104eeacb13.
Bumping manifests a=b2g-bump