Bumping gaia.json for 1 gaia-central revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-central/rev/d6da4241b6c3
Author: Mike Pennisi <mike@mikepennisi.com>
Desc: Bug 929785 - [Clock] Unable to scroll in Timer panel

Only certain UL elements should declared `overflow: auto`--those that
are explicitly intended to render with scrollbars when their content
exceeds their dimensions.

Other UL elements (i.e. the element that contains Timer settings in the
Timer panel) should not receive this declaration.

r=iliu