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

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https://hg.mozilla.org/integration/gaia-central/rev/621ff32ce43a
Author: Julien Wajsberg <felash@gmail.com>
Desc: Merge pull request #13846 from julienw/939971-sms-are-cut

Bug 939971 - [SMS] SMS are cut if you switch App while writing your text...

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https://hg.mozilla.org/integration/gaia-central/rev/f7ca7b56cefd
Author: Julien Wajsberg <felash@gmail.com>
Desc: Bug 939971 - [SMS] SMS are cut if you switch App while writing your text message r=schung

* Never add an empty text in the content array
* Remove old code that is not used anymore