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

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https://hg.mozilla.org/integration/gaia-central/rev/1a221a93b604
Author: Julien Wajsberg <felash@gmail.com>
Desc: Merge pull request #20493 from julienw/fix-homescreen-stingray-tests

Bug 1019039 - [homescreen-stingray] Intermittent Travis Unit Test failur...

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https://hg.mozilla.org/integration/gaia-central/rev/55727571d0f2
Author: Julien Wajsberg <felash@gmail.com>
Desc: Bug 1019039 - [homescreen-stingray] Intermittent Travis Unit Test failure: Applications predefined apps check state: Error: expected false to be true r=lchang

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https://hg.mozilla.org/integration/gaia-central/rev/42e094c5fd51
Author: Jim Porter <jporter@mozilla.com>
Desc: Merge pull request #20319 from jimporter/ringtones-manage-highlight

Bug 1020845 - [Ringtones] Manage Ringtones' list need a press state

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https://hg.mozilla.org/integration/gaia-central/rev/a711470a4bba
Author: Jim Porter <jporter@mozilla.com>
Desc: Bug 1020845 - [Ringtones] Ringtones list needs a press state
Bumping manifests a=b2g-bump