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

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https://hg.mozilla.org/integration/gaia-central/rev/a3afe08d57c0
Author: Greg Weng <snowmantw@gmail.com>
Desc: Merge pull request #25288 from snowmantw/bug1084530

 Bug 1084530 - [Lockscreen] The device can fall asleep too quickly after...

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https://hg.mozilla.org/integration/gaia-central/rev/915fe67c6a93
Author: Greg Weng <snowmantw@gmail.com>
Desc:  Bug 1084530 - [Lockscreen] The device can fall asleep too quickly after dialing the last digit to an emergency number
Bumping manifests a=b2g-bump