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

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https://hg.mozilla.org/integration/gaia-central/rev/c48a6acb81d9
Author: vingtetun <21@vingtetun.org>
Desc: Merge pull request #15999 from vingtetun/bug967880

Bug 967880 - [Call Log] Background doesn't scroll with the logs causing ...

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https://hg.mozilla.org/integration/gaia-central/rev/3cf8355180ad
Author: Vivien Nicolas <21@vingtetun.org>
Desc: Bug 967880 - [Call Log] Background doesn't scroll with the logs causing expensive over-invalidation. r=etienne,bgirard
Bumping manifests a=b2g-bump