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

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https://hg.mozilla.org/integration/gaia-1_4/rev/6be543fcd7de
Author: Justin D'Arcangelo <justindarc@gmail.com>
Desc: Merge pull request #21593 from justindarc/bug1028253-v1.4

Bug 1028253 - Camera App memory regression in FFOS

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https://hg.mozilla.org/integration/gaia-1_4/rev/57ffcea9f69e
Author: Justin D'Arcangelo <justindarc@gmail.com>
Desc: Bug 1028253 - Camera App memory regression in FFOS -- optimized sound resources
Bumping manifests a=b2g-bump