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

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https://hg.mozilla.org/integration/gaia-central/rev/4b9ac4671e6c
Author: James Burke <jrburke@gmail.com>
Desc: Merge pull request #15844 from jrburke/bug965363-clock-tab-select

Bug 965363 - [B2G][Clock] The tab selection bar is selectable through the create an alarm page r=mcav

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https://hg.mozilla.org/integration/gaia-central/rev/beb8a2ec50fc
Author: jrburke <jrburke@gmail.com>
Desc: Bug 965363 - [B2G][Clock] The tab selection bar is selectable through the create an alarm page
Bumping manifests a=b2g-bump