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

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https://hg.mozilla.org/integration/gaia-central/rev/ff71fccdde25
Author: Timothy Guan-tin Chien <timdream@gmail.com>
Desc: Merge pull request #24928 from timdream/softbutton-focus

Bug 1078822 - Prevent the software home button from receiving focus, r=alive

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https://hg.mozilla.org/integration/gaia-central/rev/288c308e7936
Author: Timothy Guan-tin Chien <timdream@gmail.com>
Desc: Bug 1078822 - Prevent the software home button from receving focus
Bumping manifests a=b2g-bump