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

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https://hg.mozilla.org/integration/gaia-1_3/rev/491ceeb1a118
Author: Gareth Aye <gaye@mozilla.com>
Desc: Merge pull request #18135 from gaye/bug-974554

Bug 974554 - CalDAV parser should accept ical inside xml comments nested in <calendar-data> elements r=millermedeiros
Bumping manifests a=b2g-bump