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

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https://hg.mozilla.org/integration/gaia-central/rev/1b3bf1e2e746
Author: Greg Weng <snowmantw@gmail.com>
Desc: Merge pull request #21219 from snowmantw/issue1020917

Bug 1020917 - Lock screen no longer blocks home key press

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https://hg.mozilla.org/integration/gaia-central/rev/dccc1f63ab74
Author: Greg Weng <snowmantw@gmail.com>
Desc: Bug 1020917 - Lock screen no longer blocks home key press

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https://hg.mozilla.org/integration/gaia-central/rev/dee16c605c8b
Author: Germán Toro del Valle <gtorodelvalle@gmail.com>
Desc: Merge pull request #20054 from gtorodelvalle/callscreen-bug-1018283-lockscreen-visual-refresh-reloaded

Bug 1018283 - [Follow-up 951665] Pending visual revision and adjustments of the VR call screen when in lockscreen

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https://hg.mozilla.org/integration/gaia-central/rev/efa9b56c2d73
Author: German Toro del Valle <gtorodelvalle@gmail.com>
Desc: Bug 1018283 - [Follow-up 951665] Pending visual revision and adjustments of the VR call screen when in lockscreen
Bumping manifests a=b2g-bump