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

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https://hg.mozilla.org/integration/gaia-central/rev/3ef68928e1ab
Author: Etienne Segonzac <etienne@segonzac.info>
Desc: Merge pull request #16836 from etiennesegonzac/bug-979406-early-vibrate

Bug 979406 - Don't wait 600ms before vibrating when receiving a call. r=rik

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https://hg.mozilla.org/integration/gaia-central/rev/a1df23e73aa9
Author: Etienne Segonzac <etienne@segonzac.info>
Desc: Bug 979406 - Don't wait 600ms before vibrating when receiving a call.
r=rik
Bumping manifests a=b2g-bump