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

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https://hg.mozilla.org/integration/gaia-central/rev/6c4fa19125b6
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #20034 from KevinGrandon/bug_1019070_vertical_drag_drop_edge_case

Bug 1019070 - [Vertical Homescreen] Icon could get stuck when creating and deleting groups at the same time

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https://hg.mozilla.org/integration/gaia-central/rev/a318ab1ff96a
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Bug 1019070 - [Vertical Homescreen] Icon could get stuck when creating and deleting groups at the same time

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https://hg.mozilla.org/integration/gaia-central/rev/c083c66e167f
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #20044 from KevinGrandon/bug_1018874_debug_intermittent_bookmark_test

Bug 1018874 - [Home2] Intermittent Marionette JS Failure on Travis: Vertical - Bookmark Bookmarking appends to last group

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https://hg.mozilla.org/integration/gaia-central/rev/794e3df91be2
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Bug 1018874 - [Home2] Intermittent Marionette JS Failure on Travis: Vertical - Bookmark Bookmarking appends to last group r=me
Bumping manifests a=b2g-bump