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

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https://hg.mozilla.org/integration/gaia-central/rev/506261ee4bb9
Author: Diego Marcos <diego.marcos@gmail.com>
Desc: Merge pull request #17759 from dmarcos/bug987607

Bug 987607 - [Camera][Madai] Gallery/Preview the UI takes too long to ap...

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https://hg.mozilla.org/integration/gaia-central/rev/6591b224b2b0
Author: hyuna.cho <hyuna.cho@lge.com>
Desc: Bug 987607 - [Camera][Madai] Gallery/Preview the UI takes too long to appear

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https://hg.mozilla.org/integration/gaia-central/rev/7477dbf95626
Author: Ryan VanderMeulen <rvandermeulen@mozilla.com>
Desc: Merge pull request #17671 from yzen/969553

Bug 969553 - updated the styling and markup for common tabs.

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https://hg.mozilla.org/integration/gaia-central/rev/801380ca146e
Author: Yura Zenevich <yzenevich@mozilla.com>
Desc: Bug 969553 - updated the styling and markup for common tabs. r=arnau
Bumping manifests a=b2g-bump