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

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https://hg.mozilla.org/integration/gaia-central/rev/1a93e1106012
Author: Jim Porter <jporter@mozilla.com>
Desc: Merge pull request #20505 from jimporter/ringtones-icons

Bug 1020588 - [ringtones] Update the ringtone app's icon

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https://hg.mozilla.org/integration/gaia-central/rev/28e083ca28b0
Author: Jim Porter <jporter@mozilla.com>
Desc: Bug 1020588 - [ringtones] Update the ringtone app's icon

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https://hg.mozilla.org/integration/gaia-central/rev/7606d6da01a3
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #20881 from crdlc/bug-1028817-v2

Bug 1028817 - [Collection app] Wrong box shadow in edit mode

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https://hg.mozilla.org/integration/gaia-central/rev/3722ad4472ef
Author: crdlc <crdlc@tid.es>
Desc: Bug 1028817 - [Collection app] Wrong box shadow in edit mode
Bumping manifests a=b2g-bump