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

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https://hg.mozilla.org/integration/gaia-central/rev/aa0f5b6c5342
Author: Yuren Ju <yurenju@gmail.com>
Desc: Merge pull request #20132 from yurenju/SEP

Bug 1021578 - use "$(SEP)" instead of "/" for app-makefile-template r=@cctuan

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https://hg.mozilla.org/integration/gaia-central/rev/d5b4661be82b
Author: Yuren Ju <yurenju@gmail.com>
Desc: Bug 1021578 - use "$(SEP)" instead of "/" for app-makefile-template

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https://hg.mozilla.org/integration/gaia-central/rev/5ba89766ca23
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Bug 1022693 - [UI Tests] Disable intermittent test failure: TEST-UNEXPECTED-FAIL | test_persona_app.py

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https://hg.mozilla.org/integration/gaia-central/rev/ef863a5c3ae6
Author: Diego Marcos <diego.marcos@gmail.com>
Desc: Bug 1021285 - Wallpaper Picker Screen needs a few updates r=kgrandon
Bumping manifests a=b2g-bump