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

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https://hg.mozilla.org/integration/gaia-central/rev/0ec673469eb7
Author: Greg Weng <snowmantw@gmail.com>
Desc: Merge pull request #16013 from snowmantw/issue968569-lockscreen-individual-background

Bug 968569 - [LockScreen] Set LockScreen's background as an individual element to boost performance

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https://hg.mozilla.org/integration/gaia-central/rev/1b5315d89265
Author: Greg Weng <snowmantw@gmail.com>
Desc: Bug 968569 - [LockScreen] Set LockScreen's background as an individual element to boost performance
Bumping manifests a=b2g-bump