Bumping gaia.json for 1 gaia-1_3 revision(s) a=gaia-bump

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https://hg.mozilla.org/integration/gaia-1_3/rev/38f66ad21854
Author: vingtetun <21@vingtetun.org>
Desc: Merge pull request #15989 from staktrace/nocheck-setting

Bug 967502 - Expose gaia developer setting for no checkerboarding. r=vin...