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

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https://hg.mozilla.org/integration/gaia-central/rev/a659b7a265a5
Author: Greg Weng <snowmantw@gmail.com>
Desc: Merge pull request #12600 from snowmantw/issue921335

[LockScreen] Fix the overlay blue area of the track

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https://hg.mozilla.org/integration/gaia-central/rev/4105af964ea7
Author: Greg Weng (snowmantw) <gweng@mozilla.com>
Desc: [LockScreen] Fix the overlay blue area of the track