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

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https://hg.mozilla.org/integration/gaia-central/rev/7f3e997ea214
Author: Jose M. Cantera <jmcanterafonseca@gmail.com>
Desc: Merge pull request #12880 from rnowm/917812

Bug 917812 - [Contacts] "Select All" should be "Select all" and buttons aren't vertically centered

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https://hg.mozilla.org/integration/gaia-central/rev/d21bffbe15f3
Author: rnowm <arnau@arnaumarch.com>
Desc: Bug 917812 - [Contacts] "Select All" should be "Select all" and buttons aren't vertically centered