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

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https://hg.mozilla.org/integration/gaia-central/rev/4fa2159ab340
Author: EragonJ <eragonj@eragonj.me>
Desc: Merge pull request #23054 from jwatt/master

Bug 973514 - Get rid of the dotted focus outline from Settings app sliders r=eragonj

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https://hg.mozilla.org/integration/gaia-central/rev/f43e6bf7f538
Author: Jonathan Watt <jwatt@jwatt.org>
Desc: Bug 973514 - Get rid of the dotted focus outline from Settings app sliders. r=ejchen
Bumping manifests a=b2g-bump