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

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https://hg.mozilla.org/integration/gaia-central/rev/3b717211b3f4
Author: Jed Parsons <jedp@me.com>
Desc: Merge pull request #17141 from SamPenrose/982479-CustomEvent-fix

use correct parameter for CustomEvent constructor; r=jedp

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https://hg.mozilla.org/integration/gaia-central/rev/dffee4b38bc0
Author: Sam Penrose <spenrose@mozilla.com>
Desc: use correct parameter for CustomEvent constructor
Bumping manifests a=b2g-bump