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

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https://hg.mozilla.org/integration/gaia-2_1/rev/0639054bbca4
Author: Ryan VanderMeulen <ryanvm@gmail.com>
Desc: Merge pull request #24767 from snowmantw/issue1072819-v2.1

Bug 1072819 - Lock screen fade out animation "stutters"

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https://hg.mozilla.org/integration/gaia-2_1/rev/42c78d921a4c
Author: Greg Weng <snowmantw@gmail.com>
Desc: Bug 1072819 - Lock screen fade out animation "stutters"
Bumping manifests a=b2g-bump