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

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https://hg.mozilla.org/integration/gaia-central/rev/8da6922d3f20
Author: Greg Weng <snowmantw@gmail.com>
Desc: Merge pull request #24809 from snowmantw/bug1075244

Bug 1075244 - [Lockscreen] When user changes the loc of the device and l...

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https://hg.mozilla.org/integration/gaia-central/rev/21da3c97a75a
Author: Greg Weng <snowmantw@gmail.com>
Desc: Bug 1075244 - [Lockscreen] When user changes the loc of the device and locks the screen, the time on the lock screen will go lower each time.
Bumping manifests a=b2g-bump