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

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https://hg.mozilla.org/integration/gaia-central/rev/3e34cfb78347
Author: Arnau <arnau@arnaumarch.com>
Desc: Merge pull request #17652 from rnowm/VR-modals

Bug 971072 - [VDR] [BB] update modals with new Buttons BB r=pivanov

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https://hg.mozilla.org/integration/gaia-central/rev/b697dd4c3cba
Author: rnowm <arnau@arnaumarch.com>
Desc: Bug 971072 - [VDR] [BB] update modals with new Buttons BB

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https://hg.mozilla.org/integration/gaia-central/rev/62ca208deebc
Author: Rex KM Lee <rexboy@mozilla.com>
Desc: Merge pull request #17641 from rexboy7/bug-971512-1.4

Bug 971512 - [System] Instantiable layout manager

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https://hg.mozilla.org/integration/gaia-central/rev/3966c423ac0c
Author: Rex Lee <rexboy@mozilla.com>
Desc: Bug 971512 - [System] Instantiable layout manager
Bumping manifests a=b2g-bump