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

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https://hg.mozilla.org/integration/gaia-central/rev/1d677cdfd7cf
Author: George <georgeiscoming@gmail.com>
Desc: Merge pull request #19627 from cctuan/987487-2

Bug 987487 - [Gaia] [Build] Refactoring webapp-optimize.js and unit tests

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https://hg.mozilla.org/integration/gaia-central/rev/9fe7db7c3b89
Author: cctuan <georgeiscoming@gmail.com>
Desc: Bug 987487 - [Gaia] [Build] Refactoring webapp-optimize.js and unit tests

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https://hg.mozilla.org/integration/gaia-central/rev/cb02ccefc7cf
Author: Etienne Segonzac <etienne@segonzac.info>
Desc: Merge pull request #19729 from etiennesegonzac/bug-1011312-sheet-transition-cleanup

Bug 1011312 - Cleaning up the styles of the previous sheets before r=alive

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https://hg.mozilla.org/integration/gaia-central/rev/f58562f8851e
Author: Etienne Segonzac <etienne@segonzac.info>
Desc: Bug 1011312 - Cleaning up the styles of the previous sheets before starting a SheetTransition.
Bumping manifests a=b2g-bump