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

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https://hg.mozilla.org/integration/gaia-central/rev/1d5e7f86f4fe
Author: John Hu <johu@mozilla.com>
Desc: Merge pull request #17790 from huchengtw-moz/system2/Bug_971554_reland-master

Bug 971554 - [System2] Instantiable SoundManager, r=alive

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https://hg.mozilla.org/integration/gaia-central/rev/f3b10202ecfa
Author: John Hu <johu@mozilla.com>
Desc: Bug 971554 - [System2] Instantiable SoundManager
Bumping manifests a=b2g-bump