Bumping gaia.json for 4 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/de790a9944e5
Author: Greg Weng <snowmantw@gmail.com>
Desc: Merge pull request #21661 from snowmantw/issue1036236

Bug 1036236 - [LockScreen] Unlock to Camera twice would make it unavaila...

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https://hg.mozilla.org/integration/gaia-central/rev/96dcf8e001cf
Author: Greg Weng <snowmantw@gmail.com>
Desc: Bug 1036236 - [LockScreen] Unlock to Camera twice would make it unavailable

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https://hg.mozilla.org/integration/gaia-central/rev/7fc750b6f483
Author: Yuren Ju <yurenju@gmail.com>
Desc: Merge pull request #21855 from yurenju/jsonlint

Bug 1039967 - Add json lint to verify all json files in major directories in gaia r=@cctuan

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https://hg.mozilla.org/integration/gaia-central/rev/2b6c66187480
Author: Yuren Ju <yurenju@gmail.com>
Desc: Bug 1039967 - Add json lint to verify all json files in major directories in gaia
Bumping manifests a=b2g-bump