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

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https://hg.mozilla.org/integration/gaia-central/rev/a8de55e1fb0d
Author: Sam Joch <samuel@guiora.com>
Desc: Merge pull request #14360 from samjoch/bug-924624-UserStoryAddEdgeGesturesToFTETutorial

Bug 924624 - [User story] Add edge gestures to FTE Tutorial r=arcturus

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https://hg.mozilla.org/integration/gaia-central/rev/4354edbcea3c
Author: Sam Joch <samuel@guiora.com>
Desc: Bug 924624 - [User story] Add edge gestures to FTE tutorial r=arcturus

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https://hg.mozilla.org/integration/gaia-central/rev/ee06a3fdad80
Author: Zac <zcampbell@mozilla.com>
Desc: Merge pull request #15916 from viorelaioia/bug_967012

Bug 967012 - Enable test_lockscreen_unlock_to_homescreen.py on TBPL

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https://hg.mozilla.org/integration/gaia-central/rev/b98b47edc4be
Author: Viorela Ioia <viorelaioia@gmail.com>
Desc: Bug 967012 - Enable test_lockscreen_unlock_to_homescreen.py on TBPL
Bumping manifests a=b2g-bump