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

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https://hg.mozilla.org/integration/gaia-central/rev/0898c6b2eb95
Author: vingtetun <21@vingtetun.org>
Desc: Merge pull request #15998 from vingtetun/bug967274

Bug 967274 - [Contacts] Background doesn't scroll with the contacts caus...

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https://hg.mozilla.org/integration/gaia-central/rev/3dbbbc62579e
Author: Vivien Nicolas <21@vingtetun.org>
Desc: Bug 967274 - [Contacts] Background doesn't scroll with the contacts causing expensive over-invalidation. r=arcturus,bgirard
Bumping manifests a=b2g-bump