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

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https://hg.mozilla.org/integration/gaia-central/rev/459205887170
Author: steveck-chung <schung@mozilla.com>
Desc: Merge pull request #20014 from julienw/1017024-notification-mispositioned

Bug 1017024 - [Messages] Bug 963018 change panel's default height and leads the notification mispositioned r=schung

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https://hg.mozilla.org/integration/gaia-central/rev/7b6c2f6968f1
Author: Julien Wajsberg <felash@gmail.com>
Desc: Bug 1017024 - [Messages] Bug 963018 change panel's default height and leads the notification mispositioned r=schung

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https://hg.mozilla.org/integration/gaia-central/rev/6c93638bc010
Author: EragonJ <eragonj@eragonj.me>
Desc: Merge pull request #19978 from EragonJ/bug-1018404

Bug 1018404 - [B2G][Settings][Send Feedback] The send feedback button do...

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https://hg.mozilla.org/integration/gaia-central/rev/2f2b61e939f8
Author: EragonJ <eragonj@eragonj.me>
Desc: Bug 1018404 - [B2G][Settings][Send Feedback] The send feedback button does not prompt a thank you message
Bumping manifests a=b2g-bump