Bumping gaia.json for 3 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/ec2e6d719098
Author: Zac <zcampbell@mozilla.com>
Desc: Merge pull request #20300 from zacc/bug_1019905

Bug 1019905

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https://hg.mozilla.org/integration/gaia-central/rev/28e901f6ad46
Author: Zac <zcampbell@mozilla.com>
Desc: Bug 1019906 - Update test_everythingme_search.py to vert homescreen

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https://hg.mozilla.org/integration/gaia-central/rev/1bb13056f6c3
Author: Zac <zcampbell@mozilla.com>
Desc: Bug 1019905 - Migrate test_everythingme_launch_app.py to vertical homescreen
Bumping manifests a=b2g-bump