Bumping gaia.json for 6 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/d869702f6c7b
Author: vingtetun <21@vingtetun.org>
Desc: Merge pull request #21626 from vingtetun/scroll-notifications

Bug 1035073 - Can not scroll the notifications area. r=etienne

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https://hg.mozilla.org/integration/gaia-central/rev/1e84c59415fe
Author: Vivien Nicolas <vnicolas@mozilla.com>
Desc: Bug 1035073 - Can not scroll the notifications area. r=etienne

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https://hg.mozilla.org/integration/gaia-central/rev/38827d0b42d0
Author: vingtetun <21@vingtetun.org>
Desc: Merge pull request #21620 from vingtetun/mozbrowsermetachange

Bug 1033364 - Support mozbrowsermetachange in the window manager. r=alive.

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https://hg.mozilla.org/integration/gaia-central/rev/878046349011
Author: Vivien Nicolas <vnicolas@mozilla.com>
Desc: Bug 1033364 - Add a pref to enable/disable brandcolor. r=alive

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https://hg.mozilla.org/integration/gaia-central/rev/633fd68593d1
Author: Vivien Nicolas <vnicolas@mozilla.com>
Desc: Bug 1033364 - Change window layout to accomodate custom app color for the status bar. r=alive

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https://hg.mozilla.org/integration/gaia-central/rev/7a67510fb67d
Author: Vivien Nicolas <vnicolas@mozilla.com>
Desc: Bug 1033364 - Support mozbrowsermetachange event in app_window.js. r=alive
Bumping manifests a=b2g-bump