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

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https://hg.mozilla.org/integration/gaia-central/rev/28714578feea
Author: Alive.Kuo <alegnadise@gmail.com>
Desc: Merge pull request #14635 from alivedise/bugzilla/949527/wrapper-name

Bug 949527 - Modify wrapper name, r=timdream

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https://hg.mozilla.org/integration/gaia-central/rev/21f5c547894e
Author: Alive Kuo <alegnadise@gmail.com>
Desc: Bug 949527 - Modify wrapper name

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https://hg.mozilla.org/integration/gaia-central/rev/019e7137d362
Author: Timothy Guan-tin Chien <timdream@gmail.com>
Desc: Merge pull request #14628 from timdream/splash-icon-size

Bug 904332 - Select the size of the icon in cold launch splash according to the spec, r=alive

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https://hg.mozilla.org/integration/gaia-central/rev/150eab46b1a0
Author: Timothy Guan-tin Chien <timdream@gmail.com>
Desc: Bug 904332 - Select the size of the icon in cold launch splash according to the spec