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

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https://hg.mozilla.org/integration/gaia-central/rev/42bf56dd4cf0
Author: Anthony Ricaud <anthony@ricaud.me>
Desc: Merge pull request #15359 from Rik/padding-error-960068

Bug 960068 - CSS error for padding value r=etienne

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https://hg.mozilla.org/integration/gaia-central/rev/8c243ef58119
Author: Anthony Ricaud <anthony@ricaud.me>
Desc: Bug 960068 - CSS error for padding value

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https://hg.mozilla.org/integration/gaia-central/rev/fd2374e94c5b
Author: Kevin Grandon <kevingrandon@yahoo.com>
Desc: Merge pull request #15363 from staktrace/email

Bug 958245 - Allow scrolling in textarea elements, and specifically the email compose field. r=asuth,arnau

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https://hg.mozilla.org/integration/gaia-central/rev/d1e27382d231
Author: Kartikaya Gupta <kgupta@mozilla.com>
Desc: Bug 958245 - Allow scrolling in textarea elements, and specifically the email compose field. r=asuth,arnau