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

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https://hg.mozilla.org/integration/gaia-central/rev/a38f399967b1
Author: Florin Strugariu <florin.strugariu@softvision.ro>
Desc: Merge pull request #26715 from davehunt/bug1074117-music

Bug 1074117 - Use expected conditions and optimise element lookups in music app object

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https://hg.mozilla.org/integration/gaia-central/rev/d886df0ac5a7
Author: Dave Hunt <dave.hunt@gmail.com>
Desc: Bug 1074117 - Use expected conditions and optimise element lookups in music app object. r=fstrugariu
Bumping manifests a=b2g-bump