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

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https://hg.mozilla.org/integration/gaia-central/rev/b6e1e929530d
Author: Julien Wajsberg <felash@gmail.com>
Desc: Merge pull request #14415 from julienw/fix-invalid-recipient-width

Bug 946744 - [Messages] Long invalid recipients makes the recipient pane...

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https://hg.mozilla.org/integration/gaia-central/rev/9d26171cc2d1
Author: Julien Wajsberg <felash@gmail.com>
Desc: Bug 946744 - [Messages] Long invalid recipients makes the recipient panel horizontally scrollable r=borja

Uses box-sizing: border-box to have something consistent between recipient
states