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

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https://hg.mozilla.org/integration/gaia-central/rev/121f70034b7e
Author: Greg Weng <snowmantw@gmail.com>
Desc: Merge pull request #13732 from snowmantw/issue919410

Bug 919410 - Re-implement LockScreen in Canvas to solve the glitches issue

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https://hg.mozilla.org/integration/gaia-central/rev/9912b39a212b
Author: Greg Weng <snowmantw@gmail.com>
Desc: Bug 919410 - Re-implement LockScreen in Canvas to solve the glitches issue