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

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https://hg.mozilla.org/integration/gaia-central/rev/992a79818ab9
Author: Ryan VanderMeulen <rvandermeulen@mozilla.com>
Desc: Merge pull request #15233 from Archaeopteryx/homescreen-unifyEllipsis-bug958981

Bug 958981 - [homescreen] evme-shortcut-custom=Custom... should use ellipsis. r=crdlc

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https://hg.mozilla.org/integration/gaia-central/rev/12a5d8d658f6
Author: Sebastian Hengst <archaeopteryx@coole-files.de>
Desc: Bug 958981 - [homescreen] evme-shortcut-custom=Custom... should use ellipsis

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https://hg.mozilla.org/integration/gaia-central/rev/77f27439aa4e
Author: Ryan VanderMeulen <rvandermeulen@mozilla.com>
Desc: Merge pull request #15060 from gnaneswar/Issue_951087

Bug 951087 - [Clock] Increase font-size of countdown value in Timer; r=r...

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https://hg.mozilla.org/integration/gaia-central/rev/67d325c648bd
Author: Gnaneswar Devuni <gnaneswar.devuni@accenture.com>
Desc: Bug 951087 - [Clock] Increase font-size of countdown value in Timer; r=reviews