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

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https://hg.mozilla.org/integration/gaia-central/rev/f5c34f3dea17
Author: GaryChen(pychen) <mmm198219@gmail.com>
Desc: Merge pull request #13957 from fcampo/MMS-subject-885680

Bug 885680 - Adding subject management

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https://hg.mozilla.org/integration/gaia-central/rev/d98cb7648d7c
Author: Fernando Campo <fernando.campo@o2.com>
Desc: [Bug 885680] - Adding subject management

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https://hg.mozilla.org/integration/gaia-central/rev/869754a4a338
Author: Rex KM Lee <rexboy@mozilla.com>
Desc: Merge pull request #14387 from rexboy7/fix-bug938646-2

Bug 938646 - [Dialer] Switch caller image when showing / ignoring incoming call. r=etienne

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https://hg.mozilla.org/integration/gaia-central/rev/c8f9e9dc826e
Author: KM Lee <rexboy@mozilla.com>
Desc: Bug 938646 - [Dialer] Switch caller image when showing / ignoring incoming call