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

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https://hg.mozilla.org/integration/gaia-central/rev/d15738b957db
Author: Greg Weng <snowmantw@gmail.com>
Desc: Merge pull request #22346 from snowmantw/issue1041889

Bug 1041889 - [Browser] After the lockscreen orientation change does not...

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https://hg.mozilla.org/integration/gaia-central/rev/ad049380e791
Author: Greg Weng <snowmantw@gmail.com>
Desc: Bug 1041889 - [Browser] After the lockscreen orientation change does not occur
Bumping manifests a=b2g-bump