Bumping gaia.json for 2 gaia revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/e9fc6be2c7a1
Author: Etienne Segonzac <etienne@segonzac.info>
Desc: Merge pull request #17000 from vingtetun/bug981275

Bug 981275 - Use will-change on the cards view to make it smoother. r=etienne

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https://hg.mozilla.org/integration/gaia-central/rev/115179b4c904
Author: Vivien Nicolas <21@vingtetun.org>
Desc: Bug 981275 - Use will-change on the cards view to make it smoother. r=etienne
Bumping manifests a=b2g-bump