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

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https://hg.mozilla.org/integration/gaia-central/rev/a541491b1762
Author: Ben Kelly <bkelly@mozilla.com>
Desc: Merge pull request #12778 from wanderview/contacts-render-jank

Bug 925348: Spread out contact scroll rendering work. r=arcturus

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https://hg.mozilla.org/integration/gaia-central/rev/e07c3bcdc45c
Author: Ben Kelly <ben@wanderview.com>
Desc: Bug 925348: Spread out contact scroll rendering work.

This commit avoids spikes of DOM modifications during scrolling by tweaking
the tag_visibility_monitor parameters.  The new parameters result in more
frequent updates from the monitor which spreads the resulting work out
over time during scrolling.